## 1. Brief Biography



C.I. Lewis was born on April 12, 1883 in Stoneham, Massachusetts and
died on February 2, 1964 in Menlo Park, California. He was an
undergraduate at Harvard from 1902-1906, where he was influenced
principally by the pragmatist, William James, and the idealist, Josiah
Royce. Royce also supervised Lewis's 1910 Harvard Ph.D.
dissertation " The Place of Intuition in Knowledge". While
serving as Royce's teaching assistant in logic, Lewis read
Whitehead's and Russell's *Principia Mathematica*,
a book he both admired and criticized. Later, while teaching at the
University of California at Berkeley from 1911-1920, his
principal research interests switched to logic. Lewis wrote a series
of articles on symbolic logic culminating in his 1918 monograph *A
Survey of Symbolic Logic* (SSL) (Lewis 1918) in which he both
surveyed developments in symbolic logic from Leibniz up to his own day
and presented his own modal system of strict implication. However, in
response to criticism of his account of strict implication, Lewis
deleted these sections from reprints of SSL and revised his treatment
of their topics for his co-authored 1932 book *Symbolic Logic*
(SL) (Lewis and Langford 1932) -- "the first comprehensive
treatment of systems of strict implication (or indeed of systems of
modal logic at all)", according to Hughes and Cresswell (1968,
216). 



Lewis returned to Harvard in 1920, where he taught until his
retirement in 1953, becoming Edgar Peirce Professor of Philosophy in
1948. At Harvard, Lewis' major research interest switched back
to epistemology. Starting with his much reprinted 1923 article,
"A Pragmatic Conception of the *A Priori*" (Lewis
1923), he developed a distinctive position of his own which he labeled
"conceptual pragmatism" and which he presented in a
systematic way in his 1929 book *Mind and the World Order*
(MWO) (Lewis 1929). MWO established Lewis as a major figure on the
American philosophical scene. In the 1930s and 1940s, partly in
response to the challenge of positivism, the form and focus of
Lewis' views changed, and, arguably, in subtle ways, some of the
substance. In his 1946 book *Analysis of Knowledge and
Valuation* (AKV), based on his 1944 Carus lectures, Lewis (1946)
provided a systematic and carefully analytic presentation of his
mature philosophical views. The first two thirds of the book consist
of a thorough refinement and more precise presentation of his theory
of meaning and of his epistemological views, and the last third
consists of a presentation of his theory of value.



After retirement from Harvard, Lewis taught and lectured at a number
of universities, including Princeton, Columbia, Indiana, Michigan
State, and Southern California, but principally at Stanford. His 1954
Woodbridge Lectures at Columbia and 1956 Mahlon Powell Lectures at
Indiana resulted in two last short books in ethics, *The Ground and
the Nature of the Right* (Lewis 1955) and *Our Social
Inheritance* (Lewis 1957). Lewis was the subject of a posthumously
published "Library of Living Philosophers" volume (Schilpp
1968) in which, unfortunately, his replies to critics were limited by
illness, but which, nonetheless, was an honour that indicates his
standing in and perceived significance for American philosophy in the
1950s. 



In his over thirty years at Harvard, Lewis taught some of the most
eminent American philosophers of the last half of the twentieth
century as graduate students, including W.V. Quine, Nelson Goodman,
Roderick Chisholm, Roderick Firth, and Wilfrid Sellars. Although only
Chisholm and Firth of these five were supervised by Lewis, and Sellars
left Harvard without graduating, all five refer occasionally to Lewis
in their writings, usually critically, and their own views sometimes
developed in reaction to his. (Baldwin 2007 has an excellent
discussion of the influence of Lewis on Quine, and of Lewis's
philosophy generally.)


## 2. Overview of Conceptual Pragmatism



In MWO, Lewis (1929, Chp. 1) argued that the proper method of
philosophy isn't transcendental but reflective. Philosophy seeks
to elicit the criteria or principles of the real, the right, the
beautiful, and the logically valid that are implicit in human
experience, thought, and activity. 



Lewis (1929, 37-8) believed that, on reflection and analysis, we
can distinguish three elements in perceptual knowledge: (1) the given
or immediate data of sense, (2) the act of interpreting the given as
an experience of one sort of thing as opposed to another, and (3) the
concept by which we so interpret the given by relating it to other
possibilities of experience. Our experience of the real is not given
to us in experience but is constructed by us from the data of sense
through acts of interpretation. When I know that I am looking at a
table and reflect on my experience, I realize, on analysis, that there
are certain highly specific sensuous qualities presented to me that I
am immediately aware of. Moreover, I realize that, in the light of
this and other experiences I recall, I expect, with some likelihood, I
would have certain other experiences, e.g. of feeling something
apparently hard, were I to have the experience of performing certain
acts, e.g. of reaching out with my hand. In doing so, it is the
concept of seeing a table that I am applying to my experience rather
than that of seeing a horse or that of hallucinating a table, either
of which would have involved different expectations of experience
consequent upon action. Only an active being can therefore have
knowledge, and the principal function of empirical knowledge "is
that of an instrument enabling transition from the actual present to a
future which is desired and which the present is believed to
signalize" (Lewis 1946, 4).



Statements expressing our beliefs about reality are translatable into,
and thus entail and are entailed by, an indefinitely large set of
counterfactual statements about what experiences we would have or
would be likely to have, were we to be presented with certain sensory
cues and were we to carry out further tests (Lewis 1929, 142; 1946,
180, 208). Objectively, what we actually experience may depend on the
physical circumstances of perception, e.g. lighting conditions, and
the bodily actions we perform, e.g. moving our eyes, as well, of
course, as the character of objects in our environment. However, what
matters ultimately for the meaning and confirmation of statements
about objective reality, as Lewis makes clear in AKV, are only the
"felt experience" of action and the directly presentable
sense experiences contained in sensory cues and forming the
experiential circumstances of action (Lewis 1946, 178-9,
245-6), as well, of course, as the directly presentable sense
experiences they lead us to expect. The idea of a reality neither
confirmable nor disconfirmable in principle by experience was thus for
Lewis without meaning. What distinguished his view, he thought, from
the superficially similar verification principle of meaning of the
logical positivists was his emphasis on the mediating role of agency
(Lewis 1941a, in Lewis 1970, 94). 



Whether our objective beliefs are true depends on their verifiable or
confirmable implications for future possible experience. However, in
order to guide action effectively now while saving us from the hazards
of action without foresight, empirical belief and its expectations for
experience must be justified (rationally credible, warranted) now,
antecedent to future verification (Lewis 1946, 254-7).
Justification, as opposed to verification, is the focus of AKV much
more so than MWO. Nonetheless, throughout Lewis' career from MWO
to the end, there are common claims. First, empirical knowledge
(rationally credible, justified, or warranted belief) is probable
knowledge or belief. Second, probability is a logical or inferential
relation between a conclusion or a belief and its premises or grounds.
Third, the ultimate premises or grounds relative to which a conclusion
or belief is probable, as opposed to more immediate or proximate ones,
cannot themselves be probable but must be certain (Lewis 1929,
328-9, 340-1; Lewis 1946, 186-7; Lewis 1952a).



The direct apprehension of immediately given sense presentations, and
statements expressing them, are incorrigible, indubitable, not in need
of verification, and not subject to error, and so, in these various
(and distinct) senses, "certain". (For a useful discussion
of senses of "certainty" in Lewis, see Firth 1964 and
Firth 1968 in Schilpp 1968.) However, with no possibility of error or
incorrectness to contrast with the immediate awareness of the given,
Lewis decides the normative label "knowledge"
shouldn't really be applied to it. Our objective interpretations
of experience, on the other hand, are not only fallible--given
and recalled experience doesn't guarantee the satisfaction of
our expectations about future experience--but are always subject to
revision in the light of action and further experience. Past
experience and our recollection of it play a key role in the
credibility of these interpretations. In MWO, Lewis (1929, 337) says
that memory itself is an interpretation of given present recollection,
and, as such, probable knowledge with testable or verifiable
implications for future experience. However, this doesn't
explain what warrants the interpretation and its expectations, a
*lacuna* AKV corrects. Knowing for Lewis occurs in a
non-instananeous "epistemological present" of sense
presentation embedded in a mass of recollections or sense of past
experience (Lewis 1946, 331). What is given and indubitably certain in
this present are these sense presentations and these rememberings
(Lewis 1946, 354, 362)), but what we recall of past experience is
*prima facie* and non-inductively credible for us, just because
so ostensibly remembered or recalled (Lewis 1946, 334), and thus can
serve to make our expectations of future experience rationally
credible as well. 



Despite their lack of theoretical certainty, the beliefs we form by
applying concepts to experience may count as knowledge so long as they
are true and sufficiently warranted or justified. The members of a set
of beliefs that already have some degree of confirmation or antecedent
probability in relation to present and past experience may become even
more credible if the antecedent probability of any one would be
increased by assuming the others as given (Lewis 1946, 187, 338, 349,
351, 352). The congruence of a mature system of beliefs which exhibits
this complex interlocking pattern of probability relations to each
other and to experience helps to explain how many of these beliefs can
rise to the standards for knowledge and be practically certain enough
to be counted on in action. 



Ordinary beliefs and interpretations, including perceptual beliefs,
are, for Lewis, typically the product of habit or association in which
we are guided by the elements of the given in the epistemological
present but rarely if ever attend to them. Nonetheless, the
justification of these beliefs as rationally credible requires that
there be an inferential or logical relationship of a belief or a
statement of it to grounds or reasons in experience that constitute
evidence, largely inductive, for it (Lewis 1946, 315, Lewis 1952a,
reprinted in Lewis 1970, 326). For Lewis, "the critical question
for the validity of empirical knowledge is not whether grounds
sufficient for the justification of the belief are actually contained
in the explicit psychological state of the believer, but whether the
knower's situation in empirical belief is such that sufficient
grounds could be elicited upon inquiry, or whether it is such that
this is even theoretically impossible" (Lewis 1946, 330).
Restricting the term "knowledge" to cases where grounds
are explicit would "be so rigoristic as to exclude most, if not
all, of our attempted cognitions and would obscure the important
distinction of practically valuable knowledge from
'ignorance' and from 'error'" (Lewis
1946, 330), just as restricting the term to what we are certain of
would. Nor should we think that the act of reflecting on and eliciting
what in the epistemological present justifies our beliefs loses or
takes us beyond the epistemological present (Lewis 1946, 330-2),
and thus is an impossible ideal. 



In MWO Lewis argues that probable empirical knowledge requires, on
pain of infinite regress, some *a priori* knowledge of analytic
principles explicating our concepts, the logical relationships among
them, and the criteria for applying them to experience and determining
what is real and what isn't real. Moreover, this knowledge must
be "more than probable" and "certain", which
suggests that they have a degree of warrant greater than the degree of
probability empirical considerations could yield (Lewis 1929,
311-12, 317, 321). In AKV, he also says that mathematical and
logical cognitions "may be certain" (Lewis, 1946, 29), at
least in certain cases, but he worries how they can refer to anything
beyond the cognition itself, and be classified as knowledge, if their
truth is simply the unthinkability of their falsity, given our
concepts or way of thinking. The answer is that we can be mistaken
about what is implicit in our concepts. We can fail to observe what is
implicit in our concepts and what their adoption consistently commits
us to in our thinking, and that contrast with error allows him to
classify *a priori* apprehension as knowledge. Nonetheless, any
of these mistakes is "intrinsically possible of correction
merely by taking thought of the matter" (Lewis 1946, 155)
without empirical investigation. The correctness of the principles
governing our concepts can be known *a priori*, independently
of confirmation in experience, in so far as they can be certified or
assured simply by analysis of meaning or reflection on the content of
our concepts and our explicative principles (Lewis 1946, 151,165). So,
quite apart from issues about certainty, the degree to which we are
warranted in our *a priori* apprehensions needn't
correspond to and isn't a function of their probability on the
total set of empirical considerations (cf. Lewis 1926, reprinted in
Lewis 1970, 243-4). 



What then is tested and confirmed or disconfirmed by experience is the
interpretation of experience in the light of our concepts, ordinary
empirical concepts like dog as well as more abstract categories like
causality or the concepts of logic. What isn't tested by
experience is the validity of the concepts themselves, or the logical
relationships amongst them, or the principles for applying them.
Agents bring them to experience and the only criteria they answer to
are pragmatic ones of utility or convenience (Lewis 1929,
271-2).That implies that they are also revisable on pragmatic
grounds, as Lewis himself recognizes he is doing to some extent with
the concept of knowledge itself (Lewis 1946, 27-29, 183) . 



Right at the heart of Lewis' philosophical system, then, are
several theses that weren't original to Lewis, but the critical
discussion (and sometimes rejection) of which, often in the form Lewis
gave to them, was central to much analytic philosophy in the last half
of the twentieth century. Among them are: (1) a sharp
analytic/synthetic, *a priori/ a posteriori* distinction, (2)
reductionism concerning the meaning of a physical object statement to
the actual and possible sense experiences that would confirm the
statement, (3) a foundation for all empirical knowledge in our direct
apprehension or immediate awareness of the given character of
experience and our recollections of it, and (4) the division of
experience into its given content or character, on the one hand, and
the form we impose on it, or the concepts in the light of which we
interpret it, on the other. (Quine (1951 [1953]) famously called (1)
and (2) the "two dogmas of empiricism"; Sellars (1963)
called (3) the "myth of the given"; and Davidson
(1973-1974 [1984]) called (4) the "third dogma of
empiricism", although in Lewis' mind (4) may owe more to
Kant--on whom Lewis taught a course regularly at
Harvard--than to the empiricists.)



At the same time, Lewis (1946, 9-11, 254-9) also laid down
a framework of assumptions, most explicitly in AKV, within which
analytic epistemology flourished in the last half of the
20th century: (1) knowledge is sufficiently justified
(warranted, rationally credible) true belief , (2) a belief may be
justified without being true and true without being justified, and (3)
epistemology seeks to elicit criteria or principles of justification
or rationally credibility. 


## 3. Logic and Language



In SSL Lewis (1918) surveyed and discussed developments in symbolic
logic from Leibniz to his own day and followed his discussion of
systems of material implication with a penultimate chapter presenting
his own system of strict implication (omitted from the 1960 Dover
reprint). In the concluding chapter (also omitted from the 1960 Dover
reprint), Lewis distinguished three possible types of "logistic
procedure" and resultant system (Lewis 1918, 354-62,
367-72). The first restricts proofs in mathematics to special
cases of the propositions of symbolic logic, but grants branches of
mathematics their own primitive or undefined ideas and postulates
distinct from those of symbolic logic. The second goes further,
reducing mathematics to symbolic logic by defining or analyzing the
ideas and postulates of the former in terms of those of the latter.
However, the third "heterodox" or "external"
conception of mathematics - "mathematics without
meaning" - treats mathematical and logical systems alike
as purely formal, abstract systems performing operations on
recognizable ideographic marks and strings of marks in ways that are
independent of what they denote or mean, or even the type of thing
they are interpreted as standing for, e.g. concept or proposition, and
thus independent of the truth of strings of marks. What matters
instead are simply the types of order and relation with which
recognizable marks or complexes of marks are distributed and
"extra-logical" rules or principles for manipulating them,
like the consistent substitution of marks for marks within a string of
marks. Post (1921) credited Lewis as the first to make substitution an
explicit rule for logic, whether under an orthodox conception as with
his system of strict implication (Lewis 1918, 295) between
propositions, or under a heterodox conception concerning recognizable
marks and their order (Lewis 1918, 355,358), and cited Lewis'
discussion of the heterodox conception as a stimulus for his own
formalist research.



Lewis was dissatisfied with the extensional truth functional logic
*Principia Mathematica*, and with its understanding of
implication as material implication, according to which the truth of
the if-then conditional \(p \supset q\) expressing the
material implication of \(q\) by \(p\) is a function just of
the truth or falsity of \(p\) and \(q. p \supset q\) is equivalent to \({\sim}(p \amp{\sim}q)\) and is
true just in case it isn't the case both that \(p\) is true
and \(q\) is false. As a result, among the theses of
*Principia Mathematica* are \(p \supset(q \supset p)\) and \({\sim}p \supset(p \supset q)\). In
other words, a true proposition, whatever it happens to be, is implied
by any proposition whatsoever, true or false, and a false proposition,
whatever it happens to be, implies any proposition whatsoever, true or
false. Lewis didn't deny these theses, properly understood
relative to the definition of material implication. However, he did
think that these so-called "paradoxes of material
implication" meant that material implication doesn't
provide a proper understanding of any ordinary notion of implication,
according to which one proposition implies another just in case the
latter logically follows from and is deducible from the former.



To explicate this notion he defined strict implication, according to
which the if-then conditional \(p \fishhook q\)
expressing the strict implication of \(q\) by \(p\) is
equivalent to \({\sim}\Diamond(p \amp{\sim}q)\), and is true just
in case it is not possible that \(p\) is true and \(q\) is
false. Strict implication is an intensional notion, and the logic of
strict implication is a form of modal logic. The system of strict
implication developed in SSL (Lewis 1918) was distinguished from
earlier modal logics by its axiomatic presentation in the light of the
work of Whitehead and Russell. However, Lewis faced a number of
criticisms, including one by Emil Post that one of Lewis'
postulates led to the result that it was indeed impossible that
\(p\) just in case it was false that \(p\), so that
Lewis' SSL system reduced to an extensional one. Lewis (Lewis
and Langford 1932) eliminated these problems in SL and provided
distinct systems of strict implication or modal logic, S1-S5,
each stronger than its predecessor (with S3 the system of SSL). S1
contained the following axioms:



\[\begin{align}
& (p \amp q) \fishhook(q \amp p) \\
&(p \amp q) \fishhook p \\
&p \fishhook(p \amp p) \\
&((p \amp q) \amp r) \fishhook (p \amp(q \amp r)) \\
&((p \fishhook q) \amp(q \fishhook r)) \fishhook(p \fishhook r) \\
&(p \amp(p \fishhook q)) \fishhook q
\end{align}\]


S2 adds to S1 the consistency postulate



\[
\Diamond(p \amp q) \fishhook \Diamond p,
\]


which allows one to show that if \(p \fishhook q\) is a
theorem, then so is \({\sim}\Diamond{\sim}p \fishhook{\sim}\Diamond{\sim}q\),
i.e., \(\Box p \fishhook \Box q\), expressing the
strict implication of the necessity of \(q\) by the necessity of
\(p\). S3 adds to S1 the postulate



\[
(p \fishhook q) \fishhook({\sim}\Diamond q \fishhook{\sim}\Diamond p)
\]


S4 adds to S1 the iterative axiom:



\[\begin{align}
&{\sim}\Diamond{\sim}p \fishhook{\sim}\Diamond{\sim}{\sim}\Diamond{\sim}p, \text{ i.e.,} \\
&\Box p \fishhook \Box \Box p
\end{align}\]


S5 adds to S1 the iterative axiom:



\[\begin{align}
&\Diamond p \fishhook{\sim}\Diamond{\sim}\Diamond p, \text{ i.e.,} \\
&\Diamond p \fishhook \Box \Diamond p
\end{align}\]


Critics objected that strict implication posed its own alleged
paradoxes. Within Lewis' systems S2-S5, a necessarily true
proposition is strictly implied by any proposition whatsoever, and a
necessarily false proposition strictly implies any proposition
whatsoever. However, Lewis (Lewis and Langford 1932) replied in SL
that these alleged paradoxes are simply the result of entirely natural
assumptions about valid deductive inference and entailment quite apart
from the systems of strict implication, and thus are not a problem for
the claim that strict implication provides an explication of
deducibility and entailment. (The presentation in this and the
previous two paragraphs owes much to the excellent account and
discussion of Lewis' systems of strict implication in Hughes and
Cresswell (1968, Chapters 12-13).)



Lewis thought that there are an unlimited number of possible systems
of logic. One example is the extensional propositional calculus of
*Principia* according to which there are two truth values, true
and false; other examples are the various systems of many valued logic
that Lewis surveyed in SL, and, of course, Lewis' own various
modal systems S1-S5. Lewis thought that each of these systems is
valid so long as it is internally consistent. The principles of the
various alternatives simply define the meaning of the logical concepts
and operators such as negation, truth/falsity, disjunction,
implication, and thus they are all true (Lewis 1932, in Lewis 1970,
401). Bivalent systems simply have a different notion of truth and
falsity from non-bivalent ones. Nonetheless, some systems may accord
better than others with notions of truth or implication or deduction
that are implicit in our everyday reasoning. Logics can thus be
assessed pragmatically by their sufficiency for the guidance and
testing of our usual deductions, systematic simplicity and
convenience, and accord with our psychological limitations and mental
habits. However, Lewis denied that he was claiming that principles of
logic could be true without being necessarily true, or necessarily
true without being necessarily necessary. A logic in which
\(\Box p \fishhook \Box \Box p\) holds simply
operates with a different notion of necessity from one in which it
doesn't.



Lewis (1946, Chps. 3, 6) distinguished several modes of meaning in
AKV. The *denotation* of a term is the class of actual things
to which the term applies and is distinct from the
*comprehension* -- the class of possible or consistently
thinkable things to which it applies. The *signification* of a
term is the property the presence of which in a thing makes the term
applicable, and the *intension* or *connotation* of a
term is what is applicable to any possible thing to which the term is
applicable. Intension can be linguistic intension or meaning, in which
case it is the conjunction of terms applicable to any possible thing
to which the term is applicable and thus substitutable for the term
*salva veritate*. However, since definitions must have criteria
of application and these must ultimately be non-circular, the more
basic dimension of intension is *sense meaning*. Sense meaning
is the criterion in mind in terms of sense experience for classifying
objects and applying a term-- a schema or rule that speakers have in
mind whereby a term applies to an actual or thinkable thing or
signifies some property, and which would exist even if there were no
linguistic expression for it.



Since linguistic intension is implicitly holistic and verbal
definition eventually circular, Lewis (1929, 107) said in MWO that
logical analysis isn't reduction to primitive terms, but is a
matter of relating terms to each other. Concepts consist in relational
structures of meaning. They require criteria of application in
experience and the total meaning of a term for an individual consists
of the concept it expresses and the sensory criteria for its
application. Yet, the latter needn't be identical across
individuals for there to be common concepts, Lewis argued (1929, 115).
Instead, common concepts just require shared structures of linguistic
definition and common or congruent modes of behaviour, in particular
co-operative behaviour that is guided by these concepts, a social
achievement of a common world that Lewis thought our community of
needs and interests produces. One problem with this suggestion was
pointed out by Quine (1960) in *Word and Object* with his
indeterminacy of translation argument. From the standpoint of an
interpreter, there can be alternative translation manuals or schemes
that are consistent with the total set of a speaker's verbal and
other behavioural dispositions. This is a problem that Lewis (1946,
144-5, 164) may have been aware of in AKV. In any case, in AKV
he seems to draw back from the discussion of common concepts in MWO
and to rest content with pointing out that any attribution of
linguistic meaning or sense meaning to another is inductive and thus
only probable, and any attribution of linguistic or sense meaning
similar to ours is likewise inductive, fallible, and problematic.



Lewis (1946, 84-5, 93-5) drew a sharp distinction between
analytic and synthetic truth. Analytic (or analytically true)
statements are true by virtue of the definition of the terms they
contained, and have zero intension (and universal comprehension). They
are necessarily true, true in all possible worlds, no matter what else
might be true of a world or thing, and yet are not equivalent in
meaning to each other only due to the distinct intensions of their
constituents. In MWO Lewis occasionally claimed that we create
necessary truth by adopting concepts and criterial principles; in AKV
he was more circumspect. It is a matter of convention or legislation
that a term has the meaning it does, including sense meaning, but
Lewis (1946, 155-7) denied that analytic truth was truth by
convention. "A dog is an animal" is analytically true by
virtue of the sense meaning of "dog" and
"animal", in particular, the inclusion of the criterion
for applying the latter in the criterion for applying the former, and
that isn't a matter of convention. However, Lewis never tried to
define such inclusion further. Quine (1951 [1953]) explicitly
criticized Lewis and the analytic/synthetic distinction in "Two
Dogmas of Empiricism", and would have objected to the idea of
resting the analytic/synthetic distinction on an undefined notion of
meaning inclusion. Lewis (1946, 154), on the other hand, thought that
meaning inclusion is as unproblematic and recognizable a fact as the
inclusion of one plan in another, e.g. a plan to visit France in a
plan to visit Paris, and didn't need further explication.
Nonetheless, taking meaning inclusion to be a primitive fact also
makes it more difficult to distinguish Lewis' analytic necessity
from the rationalists' synthetic necessity, despite his (Lewis
1946, 157) vigorous rejection of the latter. This is especially so
since Lewis (1946, 129) denied that analytic truth is usefully
elucidated as one that is reducible to logical truth with the
substitution of definitions. For Lewis, the adequacy of a definition
itself is a matter of analytic truth and what makes a truth a logical
truth is that it is an analytic truth concerning certain symbols.


## 4. The *A Priori* and the Analytic



Lewis (1946, 29-31) thought that necessary truths are knowable
*a priori*, independently of experience. In applying concepts
like those of red or apple to current experience, and so interpreting
experience, we form expectations and make predictions about future
experience, conditional on actions we might perform. Our beliefs
constitute empirical knowledge in so far as past experience gives us
good reason (largely inductive) for making these predictions. However,
we aren't making predictions about future experience simply in
stating what these concepts are, and what their definitions are, and
what defining criteria they provide for applying them to experience.
Such statements are explicative, not predictive, and so neither
falsifiable by failed prediction nor verifiable by successful
prediction nor justified by inductive evidence. The *a priori*
is what we are not required to abandon, no matter what experience may
bring, and in that sense, true no matter what, and in that sense
necessary (Lewis 1929, 267.) However, *a priori* principles are
neither principles that are universal nor ones that we have to accept.
The acceptance of a set of concepts is a matter of decision or
legislation or the adoption of an intention to employ certain criteria
in the interpretation of experience, something for which there are
alternatives but for which the criteria are not empirical but
pragmatic. 



In MWO Lewis (1929, 254) also thought that the *a priori*
extended to fundamental laws of nature defining basic concepts like
mass or energy or simultaneity, and thus included some of what are
typically regarded as the basic principles of a scientific theory.
Further, besides criteria like convenience and conformity to human
bent, pragmatic considerations mentioned in MWO (Lewis 1929, 267)
include factors like intellectual simplicity, economy,
comprehensiveness, and thus the overall achievement of intellectual
order. However, unlike Wilfrid Sellars and many others in the latter
half of the 20th century, Lewis never recognized such
factors as criteria of empirical justification. The reason seems to be
that Lewis (1936b, reprinted in Lewis 1970, 286) didn't think
that these factors make a hypothesis any more probable, in contrast,
presumably, to conformity to standard criteria of induction:
"What such simplicity and convenience determine is not truth or
even probability but merely simplicity and convenience, which have
their reasonable place in the choice of working hypotheses when no
more decisive criterion is presently at hand". At the same time,
he thought that the acceptance and rejection of scientific theories
wasn't entirely empirical. The choice of a system of concepts
and *a priori* explicative principles to apply to experience
and to interpret it in the light of is determined by pragmatic
considerations, not truth or probability. The simpler set of
scientific concepts and explicative principles is no more true or
likely to be true than the simpler logic is more true or valid.
Moreover, pragmatic considerations might lead us in the face of
experience to abandon our scientific concepts and *a priori*
principles explicating them without making the latter empirically
unwarranted or any less *a priori* warranted.



Empirical belief and *a priori* belief aren't logically
separated but intertwined for Lewis. The empirical belief that there
are no unicorns presupposes the concepts of negation and unicorn, and
thus more general *a priori* principles governing negation and
explicating the concept of unicorn, e.g. unicorns are horse-like
creatures with a horn in their nose. Repeatedly failing to apply the
concept of unicorn successfully to experience may make it extremely
likely that there are no unicorns and eventually lead us to drop the
concept altogether from our conceptual repertoire as useless clutter,
along with beliefs explicating the concept, but it doesn't do so
by disconfirming or making any less likely the belief that if anything
is a unicorn, it is a horned horse-like creature. More important cases
Lewis discusses are ones where we discover that there are no Euclidean
figures in our space and cease employing Euclidean geometry to
interpret experience, or ones where cruder categories for interpreting
experience are replaced by more fine grained ones that carve up
experience in novel ways that are more valuable for our purposes, or
ones where inventions open up the bounds of experience and lead us to
abandon an old theory that can accommodate such experience but in a
less simple way than a novel one. Categories for Lewis don't
really change or alter but are given up and replaced, and old *a
priori* truths are replaced by new ones, not contradicted by them
and not made false by them (Lewis 1929, 267-8). 



The most radical challenge to Lewis came from Quine (1951 [1953]) who
argued that the distinction between so called *a priori* truths
and *a posteriori* truths is just one of degree. The argument
has two steps. First, empirical hypotheses have implications for
experience only in conjunction with various empirical generalizatons
and other background assumptions, e.g. about the circumstances of
perception. Recalcitrant experience thus tells us only that some
belief or assumption in the total set that implies a contrary
experience is false, not which one, and thus any statement can be held
true, no matter what experience brings, so long as we make enough
adjustments to the rest of our beliefs and assumptions. Second,
empirical hypotheses can't logically imply anything about
experience except against a background of assumed laws of logic.
Recalcitrant experience can, in principle, then, lead us to revise an
assumed logical principle in our web of belief rather one of our other
beliefs. 



With respect to the second step, some philosophers might object that
logic is part of the framework within which beliefs have logical
implications and can't be part of the same system of belief
itself. However, Lewis himself might have trouble with this
suggestion, since he recognized the possibility of alternative logics,
and presumably, any decision, even pragmatic, about the adoption or
rejection of a logic must operate on some logical assumptions. In any
case, Lewis himself recognizes that in principle experience could lead
us to abandon logical beliefs and replace them with others. What he
will deny is that it does so by making these principles empirically
improbable, and thus any less *a priori* warranted. Arguably,
he may be assuming an excessively narrow view of what makes for
probability. 



With respect to the first step, Lewis (1946) in AKV will deny
Quine's assumption that objective statements never entail
conditionals about experience without supposing other objective
statements true and his assumption that the antecedents of these
conditionals are never themselves certain, as we shall see in the next
two sections. Moreover, objective hypotheses, despite their various
interconnections in a system of empirical belief, aren't tested
as a "block", but have separable and distinct
probabilistic connections to others (but not thereby to all) and to
experience establishing differing antecedent probabilities and degrees
of confidence, in the light of which the relevance of tests for the
probability of the various hypotheses needs to be assessed
differentially. (Lewis, 1936b, reprinted in Lewis 1970, 285-6,
Lewis 1946, 349-52). However, even so, there may be room for
alternative ways of modifying systems of hypotheses and their degrees
of credibility in the light of experience, and different responses to
probabilities that are unsettled and may change with future testing.
So, in an unpublished lecture, Lewis (1936b, 282-7) says we are
left with pragmatic factors like economy, convenience, simplicity, or
making the least alteration to beliefs, at least for the time being,
to choose "working hypotheses" even if they don't
count as empirical knowledge. Lewis (1946) omits this discussion from
AKV. Nonetheless it highlights the need for Lewis to provide a
positive account of non-empirical, non-inductive *a priori*
knowledge of principles explicating our concepts and how we have it,
not just a negative account that simply contrasts it with empirical
knowledge. 



In MWO, he says the *a priori* is knowable by the reflective
and critical formulation of our own principles of classification, at
least with respect to meaning connections explicitly before the mind
(Lewis 1929, 287-8) and in AKV that *a priori* truths are
certifiable by reference to meanings alone (and their relations like
inclusion), and tested simply by what we can think or imagine being so
(Lewis 1946, 35, 151-3). However, the only explanation he gives
of why this should warrant us in thinking anything necessary or
possible is that "as what we intend at the moment at least, a
meaning seems to be as open to direct examination as anything we are
likely to discover" (Lewis 1946, 145). It is this that warrants
us as dismissing any apparent Euclidean triangle the sum of whose
angles isn't 180 degrees as either a mismeasurement or not a
Euclidean triangle rather than a counterexample to Euclidean geometry.
Barring certainty, there seems to be a half-acknowledged,
non-inductive, basic principle of *a priori* credibility
assumed here, to the effect that if on reflection on our concepts and
meanings and classificatory intentions, we think A includes B, then we
are at least *prima facie* warranted in thinking A does include
B. In the next section, we shall see that Lewis isn't in
principle averse to non-inductively supported principles of *prima
facie* warrant. 


## 5. Empirical Knowledge



In AKV, Lewis distinguished three classes of empirical statements.
First, there are *expressive* statements formulating what is
presently given in experience and about the truth of which we can be
certain (Lewis 1946, 171-71, 183, 204, 327). Second, there are
*terminating* judgements and statements formulating and
predicting what we would experience were we to be presented with some
sensory cue and perform some action. The form of terminating
judgements is: 



> 
> If (or given) \(S\), then if \(A\), it would be the case
> that \(E\), i.e. \(((S \amp A) \rightarrow E)\), (Lewis 1946, 184, 205)
> 



where \(S, A\), and \(E\) all are formulated in
expressive language and concern particular presentable experiences
about which we can be certain, and "\(\rightarrow\)" is neither
logical entailment nor material implication but what Lewis calls
"real connection" that gives rise to subjunctive or
counterfactual conditionals. Real connections (an example of which are
causal connections) are inductively established correlations by virtue
of which one observable item may indicate another. Terminating
judgements, as expressing a general claim about a repeatable mode of
action and a sequent experience, Lewis (1946, 219) claimed, are not
decisively verifiable but are decisively falsifiable. Third, there are
*non-terminating* judgements, including *objective*
judgment, that are confirmable and disconfirmable by experience,
thanks to their sense meaning, but are neither decisively verifiable
nor decisively falsifiable. 



Objective judgements include not only perceptual judgements like
"There is a white piece of paper before me" in which we
conceptualize and interpret a given experience by relating it to other
possible experiences, but also a vast number of other beliefs about
the material world supported by our perceptual beliefs, e.g.
statements about the future outcome of space explorations, or
generalizations like "All men have noses", or non-analytic
statements about theoretical entities. Objective judgements
don't strictly imply terminating judgements of the form
\((S \amp A) \rightarrow E\) (Lewis 1946, 237).
Instead, the sense meaning of objective judgments consists of an
indefinitely large set of general probabilistically qualified
conditional judgements of the form "If it were the case that
\(S \amp A\), then, in all likelihood,
\(E\)" (Lewis, 1946, 237). Any objective perceptual
judgement \(P\) thus analytically entails and is entailed by, an
indefinitely large set of hypothetical or conditional judgements of
the form,



> 
> \((S \amp A) \rightarrow(h)E\),
>   
> 
> where \((h)E\) means that, in all probability
> \(E\), and expresses, not the probability of the conditional
> \((S \amp A) \rightarrow E)\), but "a
> relation of probability" between \(E, S\), and
> \(A\). (Lewis 1946, 250)
> 



None of these conditional judgements are decisively verifiable or
falsifiable by experience. (Lewis (1946, 247) sometimes calls the
statements that constitute the empirical content of objective
statements terminating judgements nonetheless). However, as expressing
real connections, they are nonetheless confirmable and disconfirmable
by experience, as are the objective judgements whose sense meaning
they constitute. 



For example, to use Lewis's examples, suppose \(P\) is
"a sheet of paper lies before me". Its analytic
entailments might include, "If \(S\_1\) (I were to
seem to see a sheet of paper before me) and \(A\_1\) (I
were to seem to move my eyes), then, probably, \(E\_1\)
(I would seem to see the sheet of paper displaced)", as well as
"If \(S\_2\) (I were to seem to feel paper with my
fingers), and \(A\_2\) (I were to seem to pick it up and
tear it), then, probably, \(E\_2\) (I would seem to see
or feel torn paper)", and so on. On the other hand, suppose
\(P\) is "There is a doorknob before me". Its truth
might then entail the truth of a complex set of conditionals like
"If I were to seem to see a doorknob, and were to seem to reach
out towards it and grasp it, then, probably, I would seem to feel
something hard and round", etc.



In MWO Lewis says in one place not only that appearances are
physically conditioned by objects and the physical circumstances of
one's body and perception, which is certainly a reason for
wanting to know such physical facts, but that these conditions enter
into the basic understanding or meaning of material object statements:
"It is such conditions which are expressed in the
'if' clause of those 'If ... then
...' propositions in which the predictions implicit in an
interpretation may be made explicit" (Lewis 1929, 286). However,
in AKV he explicitly rejects this position: "Thus those
conditions which are directly pertinent to a confirmation and
genuinely ascertainable are not objective facts but must be included
amongst the given appearances. They must be items of direct
presentation; and we might think of them as already covered by
'\(S\)' in our paradigm: \(S\) being given, if
\(A\) then, with probability \(M, E\)" (Lewis 1946,
246). The result is that \(S\) in Lewis' paradigm strictly
speaking won't just include the visual presentation of a
doorknob, for example, but the appearance of daylight or the feeling
of being clear headed as part of the whole presentation. Arguably,
that, together with the probability qualifier, allows him to avoid
Quine's worries about circumstances of perception and the
testable implications of empirical beliefs (Lewis 1946, 242-6).




No number of successful or failed tests will render the objective
judgement true or false with theoretical certainty. However, Lewis
thought the principle of inverse probabilities meant that the
judgement can be highly probable with a few positive confirmations,
even practically certain, in so far as the probability of \(P\) when
\(S\) and \(A\) and \(E\) obtain may approach certainty as the
improbability of \(E\) approaches certainty when \(S\) and \(A\) and
not \(P\) obtain. The principle also explains why further tests may
continue to increase our warranted assurance in the judgement even
more, though not as dramatically as earlier tests increased our
warrant (Lewis 1946, 190-92). Since confirming and gaining
assurance that \(P\) gives us assurance in all the predictions that
\(P\) entails about future experience (Lewis 1946, 239), the principle
of inverse probabilities may explain how we can act on these
predictions with increasing confidence. Even though experience of
instances of \(S\) and \(A\) and \(E\) can confirm and increase the
probability of one sensory conditional entailed by \(P\) independent
of direct experiential confirmation of the other sensory conditionals
entailed by \(P\), experiential confirmation of one conditional increases the
probability of the others, and *vice versa* (Lewis 1946, 348,
footnote 6). 



Our empirical knowledge of objects and objective events and
properties, the generalizations they support concerning patterns of
objective events and properties, and the use we make of all this for
further inductions, has a complex "many-storied
character". Nonetheless, the "whole edifice still rests at
bottom on these primitive generalizations which we make in terms of
direct experience" (Lewis 1946, 261). (Lewis (1929, 332; 1946,
261) contrasted these primitive generalizations that underlie our
objective beliefs with what he says we normally call "empirical
generalizations" that concern patterns of objective events and
may formulate natural laws supporting causal explanations.) However,
the empirical justification for these primitive generalizations and
ultimately for our objective beliefs can't rest on current sense
experience alone and requires evidence concerning the past. At the
same time, what is given to us isn't the past itself about which
we can never be certain, but just current sense presentation and
current recollection or sense of past experience. 



Lewis appreciated the problem memory posed for his epistemology much
more clearly in AKV than in MWO. In AKV, Lewis (1946, 334) argued that
whatever we ostensibly remember, whether as explicit recollection or
merely in our sense of the past, is *prima facie* credible just
because so remembered. So there are data of sense presentation and
also data of "seeming to remember" or "present
memory" (Lewis 1946, 353, 354) that constitute our ultimate
evidence, and it is only through the latter and the principle of
memorial *prima facie* credibility that empirical
generalizations and the beliefs they support can be inductively
supported by premises about past experience as well as about directly
apprehended present experience. Further the credibility of our
recollections, together with the whole range of empirical beliefs more
or less dependent on them, can be solidified and increased through the
mutual support or congruence of the whole, or can be diminished
through incongruence. 



A set of beliefs is *congruent* for Lewis (1946, 338) when the
antecedent probability of each is increased by the assumption of the
truth of the rest. A physical object statement \(P\) and the set
of sensory conditionals that constitute its content form a congruent
set, as we have seen. Indeed, by virtue of exhausting the empirical
content of \(P\), Lewis (1946, 348-9, footnote 6) thinks
the sensory conditionals constitute a congruent set by themselves. In
any case, the degree of warrant enjoyed by the various elements of a
mature system of empirical belief, especially one that counts as
*knowledge*, depends on the inferential support the elements
provide each other and the total empirical and memorial data present.
However, Lewis emphasizes that for the members of a congruent system
to have any degree of probability, "it is absolutely requisite
that some at least of the set of statements possess a degree of
credibility antecedent to and independent of the remainder of those in
question, and derivable from the relation of them to direct
experience" (Lewis 1946, 339).



As a result, the "whole
intricate network" of the empirically credible, Lewis notes,
"will be constituted at bottom by linkages of ground and
consequence, which is in general a one way relation" (Lewis
1946, 351). Disentangling the network would reveal particular linkages
of *prior* probability relationships that would confer some
degree of initial probability not just on what we recall of past
experience but on simple generalizations from past experience and the
expectations of future experiences and thus interpretations of
experience these recollections inductively support, even in the
hypothetical absence of (other) objective beliefs with which they are
congruent. Moreover, the recollections that support them and form part
of an overall congruent system must have some degree of credibility
independent of each other and the rest. The improbability of
independently probable congruent recollections all being true were the
beliefs they inferentially support and that inferentially support them
not true makes it unlikely that they are illusions of memory and
increases the initial probability enjoyed antecedently by the
recollections and what they support (Lewis 1946, 352-3).
Spelling out the antecedent and independent probability constraints is
tricky, to which Lewis devotes an extended discussion (Lewis 1946,
332-57). 



The principle of the *prima facie* credibility of mnemic
presentation of past experience can't itself be justified
inductively for Lewis, on pain of circularity. Nor did he think it is
simply a postulate -- something we have to assume for empirical
knowledge to be possible. Instead, he argued that it is constitutive
of the lived world of experience and something for which there is no
meaningful alternative. Sceptical alternatives designed to undermine
the principle are ones that are inaccessible to knowledge and thus
ones for which there is no criterion in experience. So it is an
"analytic statement" that the past is knowable, and a
similar claim was made for the relevance of past experience to the
future, and thus for the knowability of empirical reality. The
philosophical problem for Lewis (1946, 360-2) is to formulate
correctly the criteria that "delimit empirical reality and
explicate our sense of it". 



In MWO, he defended induction in more detail by arguing that not every
prediction is compatible with an evidence base, and that successive
revision of one's predictions in the light of new experience
can't help but make for more successful predictions (Lewis 1929,
367, 386). Nelson Goodman's well known "grue"
example (Goodman 1955) poses problems for the relevance of the first
claim and the force of the second. At other times, Lewis simply
followed Hans Reichenbach in claiming that we can be assured only that
if any procedures will achieve success in prediction, inductive ones
will, without clearly distinguishing that claim from any attempt at an
analytic justification of induction.



Rationally credible or warranted or justified belief, Lewis thought,
is probable on the evidence, but the presentation of his views on
probability was underdeveloped in MWO, and complex, and sometimes
confusing, in AKV. In AKV, Lewis defended an *a priori* account
of probability or what he sometimes called *expectation*.
However, he rejected the Principle of Indifference often associated
with *a priori* accounts, understood as the principle that in
the absence of any reason for thinking one *a priori*
possibility more likely than another, they are equiprobable (Lewis
1946, 306-314). The expectation or probability
\(a/b\) of a proposition \(P\) is always relative
to some set of empirical data or premises \(D\). The expectation
corresponds to an *a priori* valid estimate of the frequency of
some property mentioned in \(P\) in some reference class
mentioned in \(P\) , which estimate is derived from data or
premises \(D\), given the *a priori* valid principles of
probabilistic inference, including the principles of induction.
Hypothetical or conditional probability statements that are *a
priori* valid license valid probabilistic inferences from premises
about evidence or data to probabilistic conclusions. However, for
Lewis, both hypothetical and categorical probability are always
relativized to an evidence base, despite his occasional apparent talk
of *a priori* valid probability statements as licensing
inferences from empirical evidence to a (detachable) conclusion
"Probably, P".



Lewis rejected the view that probabilities are empirically based
estimates of the limiting value of the frequency of instances of a
property in a population, and thus expressed in non-terminating
judgments. First, he thought that any attempt to define probabilities
as the ratio of instances of one property among instances of another
property as the latter approaches infinity would make probability
judgments empirically untestable. Second, he argued that, if
probability judgements were empirical frequency claims, then the
probability judgements would themselves only be probable, something
that can't be coherently accounted for. Nonetheless, Lewis
recognized the need to assure ourselves rationally that the frequency
as validly estimated from the data is closely in accord with the
actual frequency and that there is nothing in the case at hand
affecting the occurrence of the property which isn't taken into
account in the specification of the reference class. Lewis dubbed this
the *reliability* of the determination of probability or
expectation. He thought that reliability is a function of the adequacy
of data (e.g. size of sample), the uniformity with which the frequency
of some property in the data as a whole also holds for subsets of the
data, and the *proximateness* or degree of resemblance of the
case at hand in P to the data, all of which he also thought are
logical relations.



Thus, in AKV, Lewis (1946, 305) claimed that the full statement of a
probability judgement should be of the form "That \(c\),
having property \(F\), will also have property \(G\), is
credible on data \(D\), with expectation \(a/b\)
and reliability \(R\)", and is assertable in whatever sense
\(D\) is. The judgement is valid when, in accordance with the
*a priori* rules of probability and the correct rules of
judging reliability, \(D\) gives the estimate
\(a/b\) of the frequency of \(F\)s among
\(G\)s, and \(D\)'s adequacy, uniformity, and
proximateness to the case in point, yields reliability \(R\). A
valid probability judgement is true when \(D\) is true, and is a
categorical rather than a hypothetical judgement when \(D\) is
categorically asserted as true. The assertion of the empirical data
\(D\) is the only empirical element in the probability judgement,
which otherwise has no testable implications for experience. However,
the belief \(P\), that \(c\) which has \(F\) is also
\(G\), is an empirical belief that may be rationally credible,
empirically justified, and warranted, in so far as \(D\) is given
and the degree of assurance or belief corresponds to an *a
priori* degree of probability (expectation) of \(P\) on
\(D\) that is sufficiently reliable. Further, acceptance of
\(P\) counts as empirical *knowledge* in so far as,
firstly, \(P\) is true, secondly, the degree of probability or
expectation of \(P\) on \(D\) is sufficiently high as to
approach practical certainty, and, thirdly, \(D\) consists of all
relevant data (Lewis, 1946, 314-15).



It is important to distinguish probabilistically qualified
counterfactual statements of the form \((S \amp A)
\rightarrow(h)E\) from *a priori* probability
statements of the form \("\text{Prob}(E, \text{ on } S \text{ and }
A) \gt .5".\) Both express conditional probabilities.
However, the former express 'real' connections knowable by
induction from past experience (Lewis 1946, 250). They constitute the
analytically entailed consequences of an objective material objective
statement \(P\), but can't themselves be analytic truths.
The latter, on the other hand, if true, are analytically true,
knowable *a priori*, with zero intension, and entailed by any
statement whatsoever, and so can hardly constitute the empirical
meaning of contingently true material object statements. Yet, apart
from denying that "\(\rightarrow\)" can be understood either as
material implication or strict implication, Lewis had little to say in
print about what the truth conditions of subjunctive or counterfactual
conditionals are. Murphey (2005, 332) quotes correspondence from Lewis
complaining that Goodman and Chisholm in their writings miss the
obvious interpretation of "If \(A\) were the case, then
\(B\) would be the case", namely that \(A\) plus other
premises of the (actual or hypothetical) case inductively justify the
conclusion \(B\). Lewis needs to say more then about what, if
anything, distinguishes \((S \amp A) \rightarrow E\) from \((S \amp A) \rightarrow 
(h)E\). Is it the degree of probability of \(E\)
on the premises, practically certain in the former case, only somewhat
probable in the latter? Another problem is to interpret the remark so
as to avoid turning counterfactuals into *a priori* analytic
truths, albeit ones concerning probabilities. Nonetheless, Lewis
emphasized their importance, and the importance of the real
connections they express, for the possibility of realism about the
material world and the rejection of any sort of idealism or view that
physical objects are simply mind-dependent collections of experiences
(Lewis 1946, 226, Lewis 1955, in Lewis 1970). The sensory conditionals
\((S \amp A) \rightarrow E\) and \((S \amp A) \rightarrow(h)E\) can be true, as can the
material object statement \(P\) that entails them, quite apart
from the truth of the expressive statements \(S\) and \(A\).




Chisholm (1948) raised an important challenge to Lewis' claim
that a physical object statement \(P\) entails a set of
counterfactual statements expressing claims about what experiences one
would have or would be likely to have were one to (seem to) carry out
certain tests upon being presented with certain sensory cues. If
\(P\) entails \(T\), then for any \(Q\) consistent with
\(P, P\) and \(Q\) also entail \(T\). However,
Chisholm argued, for any material object statement \(P\) and for
any sensory conditional \((S \amp A) \rightarrow 
(h)E\), there will be some other material object
statement \(M\) about the circumstances of perception that is
consistent with \(P\), such that \(P\) and \(M\) can
both be true while \((S \amp A) \rightarrow 
(h)E\) is false. For example, suppose \(P\) is
"There is a doorknob before one" and \((S \amp A) \rightarrow(h)E\) is "If one were to
seem to see a doorknob and have the experience of reaching out with
one's hand, then, in all likelihood, one would seem to feel
something hard and round", and \(M\) is "One's
fingertips have been permanently anaesthetized". (Expanding the
understanding of \(S\) to include sensory correlates of
circumstances of perception, as Lewis (1946, 245-6) suggests,
presumably just requires expanding the understanding of \(M\)
with some imagination.) A material object statement like \(P\),
therefore, doesn't entail sensory conditionals like \((S \amp A) \rightarrow(h)E\) . Instead of
Lewis' empiricism about the meaning and justification of
material object statements, Chisholm proposed that our spontaneous
perceptual beliefs about the world, e.g. that one is seeing a
doorknob, are *prima facie* justified just by virtue of being
such spontaneous perceptual beliefs, quite apart from any inductive
justification from present and past experience that might be
reconstructed. Lewis' own defence of the *prima facie*
credibility of memory, Chisholm thought, prepared the way for his
alternative. Quine (1969), on the other hand, thought that
Chisholm's problem just shows that what have consequences for
experience and are tested by experience are never individual material
object statements in isolation from each other but only sets of them
or theories. Quine saved empiricism by drawing a holistic moral from
the sort of problem Chisholm posed. 



In a rare reply to critics, Lewis (1948, reprinted in Lewis 1970,
322-3) objected that Chisholm had misunderstood the implication
of the probability qualifier. The familiar rule "If \(P\)
entails \(T\), then for any \(Q, P\) and \(Q\)
entail \(T\)" doesn't apply, he claims, when
\(T\) is any kind of probability statement. \(E\) not being
probable on \(P\) and \(M\) and \(S\) and \(A\) is
perfectly consistent with \(E\) being probable on \(P\) and
\(S\) and \(A\) and its truth doesn't undermine the
truth of the claim that \(P\) entails \((S \amp A) \rightarrow(h)E\). Chisholm might respond that
the familiar rule is simply a consequence of the meaning of entailment
or strict implication, according to which it is not possible that
\(P\) and not \(T\). Furthermore, Lewis isn't simply
asserting that \(E\) is probable on \(P\) and \(S\) and
\(A\), but, as Lewis (1946, 248-50) himself says in his
formal summary of his view, that the subjunctive conditional
\((S \amp A) \rightarrow(h)E\) is an
*analytic consequence* of \(P\), at least in the way \(X\)
*is coloured* is a consequence of \(X\) *is red*, and is
(strictly) implied by \(P\), as a conclusion to a premise, even
if not solely by reference to the "rules of deductive
logic". Of course, "\(P\) strictly implies
\(((S \amp A) \rightarrow(h)E)\)"
itself strictly implies "\((P \amp S \amp A) \rightarrow(h)E\) " (but not
conversely), and neither is contradicted by "\((P \amp S \amp A \amp M) \rightarrow\)
not\((h)E\)". However, \((S \amp A) \rightarrow(h)E\) expresses in its own right
an "in all likelihood" relation of probability between
\(E\) and the possibly counterfactual \(S\) and \(A\)
(Lewis 1946, 250), quite apart from \(P\), a relation that, for
Lewis, holds when it is in accord with the *a priori* rules of
probability (including inductive inference) relative to the empirical
data D (Lewis 1946, 305,314), e.g. in the simplest case, recollections
of past instances of \(E\) usually following \(S\) and
\(A\). Chisholm's challenge seems to remain, whether it is
possible for \(P\) and \(M\) to be true and \((S \amp A) \rightarrow(h)E\) false. 



Nonetheless, as Lewis (1948, reprinted in Lewis 1970, 318-321)
notes in a breakdown of cases, the probabilistically qualified
subjunctive \((S \amp A) \rightarrow 
(h)E\) ("If one were to seem to see a doorknob
and have the experience of reaching out with one's hand, then,
in all likelihood, one would seem to feel something hard and
round") is compatible with occasional failures of prediction.
Thus, he can point out that in cases where the truth of \(M\)
("One's fingertips have been permanently
anaesthetized") somehow doesn't affect the sensory cues
and is recent enough to have not (yet) significantly altered the
patterns in the data D, e.g. of instances of \(E\) usually
following \(S\) and \(A, (S \amp A)
\rightarrow(h)E\) remains true when \(P\)
("There is a doorknob before one") and \(M\) are
true. That's because in such cases \((S \amp A)
\rightarrow(h)E\) is still supported by the extant data of
experience and memory D in accord with the *a priori* rules,
despite the truth of \(M\), and the reliability of that
probability assessment is still warranted by the data and rules for
judging reliability, although \(M\) might affect the actual
reliability of the probability assessment in the cases at hand, and
might eventually affect the actual frequency of \(E\) over time.
Much depends here on the understanding of probability statements and
conditionals, and Lewis' account isn't without its
tensions. In different (but more normal) cases where \(M\) does
manifest itself by affecting the sensory cues, making \(S\_1\)
true, for example, one seems to have tingly, numb fingertips, in
addition to \(S\), one seems to see a doorknob, \((S \amp S\_1 \amp A) \rightarrow\) not \((h)E\) might
indeed be true, but, as Lewis would emphasize, it is consistent with
\((S \amp A) \rightarrow(h)E\). Finally,
in yet different (and bizarre) cases where the longstanding truth of
\(M\) when \(P\) was true in the past didn't affect
the sensory cues but significantly affected the pattern with
\(E\), making D1, e.g. \(E\) not usually following
\(S\) and \(A\) in recalled instances, the actual empirical
data, rather than D as in the first case, it seems that D1
wouldn't have led us to expect \(E\) upon \(S\) and
\(A\). However, that expectation is constitutive in part of our
objective thought \(P\), and thus, as Firth (1950) suggests, the
failure of the sensory conditional \((S \amp A)
\rightarrow(h)E\) to hold relative to D1 is arguably
irrelevant to its entailment by the thought we express by
"P". In any case, one might wonder how sensory
conditionals like \((S \amp A) \rightarrow 
(h)E\), which, for Lewis, express generalizations
concerning what any one would (likely) experience and which must do so
if they are to provide the empirical content of objective judgements
about an interpersonal material world, can nonetheless be warranted
inductively by premises concerning only patterns in the personal
experience of the putative knower, in particular how their probability
can be judged to be sufficiently reliable, without reference to any
background beliefs about how the material world interacts with persons
generally and their bodies to affect experience. 



Yet, if Lewis were simply to drop the analytic entailment claim that
gives probabilistically qualified sensory conditionals like \((S \amp
A) \rightarrow(h)E\) a privileged semantic role, and rest content with
the various consistent probability statements relating \(E\) to \(P\),
\(S\), \(A\), and \(M\), the character of his empiricism would become
puzzling. If the consistent relative probability statements in
question are the probabilistically qualified subjunctive conditionals,
\("(P \amp S \amp A \rightarrow(h)E"\) and
\("(P \amp S \amp A \amp M) \rightarrow \text{not}(h)E)",\) then the statements in question are empirical
propositions justified by induction. The justification for them thus
will presuppose prior knowledge of the truth of material object
statements like \(P\) and \(M\), perhaps in the way Chisholm suggests,
rather than explain why and how we can know such propositions solely
on the basis of present and past experience of the given. On the other
hand, if the relative probability statements are
*a priori* analytic statements in their own right, then it is
the total set of such statements that will constitute the empirical
meaning of \(P\), statements like



\[
 "\text{Prob}(E, \text{ given } P \amp S \amp A \amp M) \lt .5"
\] 

as much as



\[
"\text{Prob}(E, \text{ given } P \amp S \amp A\gt .5",
\]


thus including statements containing other
material object statements like \(M\). Even when the relativization to
other background material object statements isn't explicit, the
probability statement would seem to be implicitly relative to some
background assumption of material normality. In other words, Lewis
would have abandoned reductionism for Quine's holistic
conclusion that individual material object statements like \(P\),
apart from other material object statements, have "no fund of
experiential implications to call their own" (Quine 1969,
79).



As noted earlier, Lewis (1929, 286) and Lewis (1936b) flirts with a
version of Quine's alternative. However, in AKV and in his reply
to Chisholm, Lewis clearly repudiates it: if Chisholm were right that
"no statement of objective fact had consequences for direct
experience without further premises specifying objective conditions of
perception", then, Lewis says, "the type of empiricism of
which my account is one variant--verification-theories and
confirmation-theories--will be altogether indefensible"
(Lewis 1948, reprinted in Lewis 1970, 318). The result, he adds, would
be a fatally flawed "coherence theory of empirical truth"
that leaves us with "nothing..but skepticism". 


## 6. The Given



Lewis' views about the given are at once among his best known
and among his most criticized. The pre-analytic datum for
philosophical reflection is our "thick" experience and
knowledge of the world around us, but reflection on this experience
and knowledge reveals two elements: the given or immediate data of
experience and the activity of thought whereby we conceptually
interpret the given. The given in sense experience consists of
specific sensuous qualities that we are immediately aware of when, for
example, we take ourselves to be seeing or hearing or tasting or
smelling or touching something, or even to be hallucinating or
dreaming instead. These distinct qualities or *qualia*
(singular *quale*) are the repeatable felt characters of
experience, and include the felt goodness or felt badness of
particular experiences or stretches of experience, as well as
qualities of sight, sound, taste, smell, touch, motion, and other
familiar modes of experience. On the other hand, the repeatability of
these qualities, or the similarity of current instances to past
instances, isn't something that is given to us. When we
conceptually interpret the given, we form hypothetical expectations
and make predictions, in the light of past experience, concerning
experiences we would have were we to engage in specific actions, and
so, in applying concepts, as Kant suggests, we relate our experiences
to each other. However, usually, we do so automatically and without
conscious reflection, in ways that express habitual attitudes and
associations rather than engaging in (explicit) inference. The given,
unlike our conceptual interpretation of it, isn't alterable by
our will. It consists of what remains when we subtract from ordinary
perceptual cognition all that could conceivably be mistaken (Lewis
(1946), 182-3). Our apprehension of the given isn't,
therefore, subject to any error and isn't subject to correction
or verification or disconfirmation from further experience, and
isn't, as a result, to be classified as knowledge. Any
comparative classification of experience in terms of similarities and
differences with other experiences, on the other hand, relates
experiences to each other and and isn't certain. What we recall
of past experience, even immediately, isn't given to us or
certain, but, as Lewis makes clear in AKV, our immediate recollection
or sense of past experience as having been so and so is. 



In MWO, Lewis (1929, 401) says that the given in experience never
occurs in the absence of interpretation and characterizes the
distinction as an "abstraction" of elements that are
synthesized in our judgment, but which we may realize are common to
quite different conceptualizations such as those of the adult and the
child (Lewis 1929, 49-50). AKV is more circumspect. Although the
given is what we are immediately aware of or directly apprehend as it
guides and corrects our interpretations, it isn't something we
focus on or attend to or are "clearly conscious"of in our
automatic interpretations (Lewis 1946, 153) any more than in riding a
bicycle we attend to or focus on the various sensory and motion and
balance sensations that are elements in and guide our activity, though
we could on reflection and perhaps did in learning (Lewis 1946, 10).
In perceptual cognition, what is given in sense experience serves as a
natural sign of future experience contingent on action in the light of
past experience, and prompts the anticipation of such experience. What
is given is of no interest to active beings apart from what it
signifies for future experience and anticipations it prompts for
action. (Lewis 1946, 10). 



Nonetheless, Lewis (1952a, reprinted in Lewis 1970, 326) says
"the *validity* of this interpretation is that and that
only which could attach to it as an inductive inference from the given
visual presentation...the incorrigible presentational element".
What matters for the credibility or warrant or validity of the belief
is that there is a logical, inferential relation between the belief
and grounds in experience that prompt it in the light of past
experience and that can be elicited on critical reflection and the
character of the relation made clear enough for our theoretical
purposes. However, the credibility or validity of the belief
isn't created by the reflective attempt to elicit sufficient
grounds (Lewis 1946, 186, 189, 262, 329-32) The given, thus,
plays both a causal role as the ultimate or remote ground responsible
for belief and an epistemic role as the ultimate justifying grounds of
empirical belief. (Lewis 1946, 262, 328-30). 



Probability, for Lewis, concerns a logical relation between a
conclusion and premises, and a statement is categorically assertable
with a degree of probability or credibility, or a belief warranted or
credible to that degree, as opposed to being merely hypothetically
probable *a priori* to that degree on premises, only to the
extent that the premises or data are sufficiently credible or
warranted or probable. (Lewis 1946, 315-27). Ultimately, the
conclusion must be warranted or credible or probable on premises or
data that are certain, not just true, and that are not just warranted
or credible only on other premises or data, even if we may never reach
these ultimate premises ordinarily in showing probability or
justification. Otherwise we have "an indefinite regress of the
merely probable...and the probability will fail to be genuine"
(Lewis 1946, 186). Here he echoes MWO where he says that the validity
of a probability judgement is a relation between the judgement and
"ultimate premises" that (a) "may verbally be quite
remote", unlike the "immediate premises" we might
initially and normally cite, that (b) must be a
"certainty" rather than merely probable on yet further
premises, and that (c) must be "actual given data for the
individual" (Lewis 1929, 328-9). Lewis is defending a
normative standard for empirical knowledge that he thinks is implicit
in cognition and revealed on reflection but which is also
psychologically and verbally remote from everyday cognitive practices
of justifying beliefs to ourselves or others in the light of more
proximate assumptions taken for granted in the context of inquiry or
discussion. Some pragmatists might feel there is tension here. 



In MWO, Lewis (1929, 53) also famously says that the given is
"ineffable". So how can what is ineffable even be true,
and how can what is neither true nor false, nor as a result, neither
probably true nor probably false, serve as the ultimate premises of
*a priori* valid logical probability relations licensing
belief or assertion with probability or credibility? And how can we
anticipate or predict future experience that isn't yet given,
except in conceptual or comparative terms that won't allow for
decisive falsification? Again, there may seem to be tension in
Lewis' views of the given and the epistemic role he assigns it.
Lewis (1936a and 1936b, reprinted in Lewis 1970, 155-7,
292-3) clearly recognizes the logical and epistemological
problems, and he responds by introducing categories of
*expressive* statements and the *expressive* use of
language. This carries over into AKV. Expressive statements like
"It seems as though I am seeing a red round thing" serve
to convey or express or *denote* what we directly apprehend in
experience without conceptualizing and interpreting it. They are true
by virtue of the qualitative character of experience they express and
are verified by it, and false only when we knowingly lie about our
experience, and the ineffability of what they express just consists in
their not implying possibilities of further experience. Moreover,
their truth is something that we know, or, as he more carefully and
repeatedly says in AKV, something about which we are certain (Lewis
1946, 171-2, 183, 204, 327). The expressive use of language is
to convey or express what is not only directly apprehended but what
may be directly apprehensible in the future or, perhaps, was directly
apprehensible in the past. (Lewis 1946, 179). Nonetheless, Lewis notes
that the expressive use of language is needed only for the discussion
of knowledge, not for knowledge itself (Lewis 1946, 183; 1952a,
reprinted in Lewis 1970, 327). So perhaps it isn't surprising
that later he also talks of "immediately given facts of
sense" and "facts of our seeming to remember" (Lewis
1946, 327, 353) and "datum facts" and "logical
relations of facts" (Lewis 1952a, reprinted in Lewis 1970, 325).




Sellars (1963, 132) thought that the classical empiricist given was an
inconsistent triad of three claims: (1) being appeared to as if there
were something red entails non-inferentially knowing that one is
appeared redly to, (2) the ability to be appeared to is unacquired,
and (3) the ability to know facts of the form x is F is acquired.
Lewis clearly denied (1), but he recognized this was the result of a
choice about how to use "know" and that others,
"without fault", might choose to extend it to direct
apprehensions of sense because they are certain for us (Lewis 1946,
183). However, if Lewis followed suit and granted (1), it seems he
would deny (3) on the grounds that the ability to be certain of the
given wasn't acquired. Sellars might question whether such
certainty, or the expressive language in which it was couched, was
sufficiently rich in content to support other knowledge inferentially.
In any case, Lewis' defense of the certainty of the given rests
on two claims. First, it is just an undeniable fact, apparent to
anyone who reflects on experience, that there is a sensuous character
of experience which we are aware of and can't be mistaken about
and which, until it fades to memory, isn't subject to correction
and isn't further confirmable. As Lewis (1952a, reprinted in
Lewis 1970, 329) put it in his symposium on the given with Reichenbach
(1952) and Goodman (1952), there is no requirement of "inductive
consistency" on protocols or expressive statments. Second, the
supposition that probability is always relative to something else that
is itself only probable means that probabilities can never get off the
ground. As Lewis famously says, "if anything is to be probable,
something must be certain" (Lewis 1946, 186). Goodman (1952), in
his symposium contribution, argued that the premises relative to which
other statements are credible or probable just have to be initially
credible on their own to some degree, not certain, though subject to
future confirmation or disconfirmation in the light of further
experience. So long as they are initially credible on their own rather
than because something else is initially credible, Lewis'
regress fails. This is a view that attracted many epistemologists
after Lewis in some form or other. 



Lewis' response is instructive for his understanding of
epistemology. For Lewis (1952a, reprinted in Lewis 1970, 330), a
principal task of epistemology is with the "validity" of
knowledge, that is to say with the justification or warrant for
cognition that distinguishes empirically warranted belief from lucky
or unlucky guess or hazard of belief. If a class of beliefs in
principle may be false, we need some reason or grounds for thinking
its members true or likely to be true, especially if we plan to base
other beliefs on them. That requires present or past justifying
grounds of belief, not just future potential for verification or
confirmation as he thinks Goodman proposes. Otherwise, we confuse
justification with verification, or ignore the former for the latter.
Nor can the grounds consist solely in other beliefs that might be
mistaken without grounds for thinking them true or likely to be true,
or in beliefs that stand in conditional probabilistic relations to
each other, as he thinks Reichenbach proposes, without any antecedent
probabilities deriving from something else (Lewis 1952a, reprinted in
Lewis 1970, 328). Lewis acknowledges that his (somewhat traditional)
concerns with validation or justification, skepticism, and the need
for given justifying grounds, lead him to depart from or supplement
standard pragmatic theories. 



Finally, we can't directly verify the existence of other
subjects of experience or what is given to them in their experience.
Nonetheless, Lewis (1934, 1941b) claimed that by empathy, in terms of
our own conscious experience, we can imagine or envisage the conscious
experience of others, rather than simply our own experience of others
and their bodies and our interactions with them. Moreover, the
supposition of another consciousness like ours, with a body like ours,
can be indirectly confirmed and supported by induction. However, Lewis
provided no details concerning this inductive support for our belief
in other minds. 


## 7. Action, the Good, and the Right



In contrast with those logical positivists who thought that statements
of value merely express attitudes, *pro* or *con*, to
objects, persons, or situations, but are neither true nor false, Lewis
(1946, 396-98) thought that statements of value were as true or
false as other empirical statements, and every bit as empirically
verifiable or falsifiable, confirmable or disconfirmable. True, felt
value *qualia*, felt goodness and badness, are given to us and
directly apprehended in experience or stretches of experience, and
"expressive" statements must be used to indicate or convey
them. However, such statements, like Lewis' other
"expressive" statements, may be true or false (see
previous section), and simply convey the occurrence of given
*qualia* in experience and no more, instead of indicating the
existence of objects, situations, or persons, and expressing our
attitudes to them. Moreover, there are also for Lewis terminating
judgments of value concerning what the felt value of some experiences
indicates about the felt value of further experiences. Finally, there
are "objective" judgements of value: judgements
attributing value to persons, objects, and objective situations, in so
far as they have the potential, depending on circumstances, to produce
felt goodness or badness in us or others. These are non-terminating
judgements of value and are empirically confirmable or disconfirmable
by induction just like any other objective empirical judgement. Lewis
thus claims that his theory of value is thoroughly naturalistic and
humanistic, rather than transcendental, but still objectivist. 



The felt goodness of experience is what is intrinsically good or
valuable for its own sake. It is only experience in so far as it has
such value quality that is intrinsically good rather than merely
extrinsically valuable for its contribution to something else that is
intrinsically valuable. Value and disvalue are modes or aspects of
experience to which desire and aversion are "addressed"
(Lewis 1946, 403). Lewis denies that "pleasure" is
adequate to the wide variety of what is found directly good in
experience, and thus thinks it inadequate as a synonym for
"good". However, as Frankena (1964) argues, for Lewis
directly found goodness still seems to be as natural a quality or
property of certain experiences as any other *qualia* directly
apprehended in experience. Nonetheless, the value of a stretch of
experience, indeed a whole life, isn't just the value (and
disvalue) of the parts, and in AKV, Lewis criticized Bentham's
attempt at a calculus of values. For Lewis, the intrinsic value found
in the experience of a symphony isn't just the sum of the
intrinsic value of the movements taken individually, but reflects the
character of the symphony as a temporal *Gestalt*. What is
*ultimately good* for Lewis is the quality of a life found good
in the living of it. (Lewis 1952b in Lewis 1970, 179) The constituent
experiences thus might have value for their own sake, but also value
for their contribution to the value of the whole life of which they
are parts.



However, Lewis thought that judgements about how a valued experience
contributes to the value of a life as a whole, unlike some terminating
judgements about how one valued experience will yield another valued
experience, are not decisively verifiable or falsifiable. First, any
attempt to apprehend a life as a whole and the value of it as
experienced goes beyond the specious present of experience and relies
on memory and expectation of past and future experience and their
values, and thereby leaves room for error. Second, any attempt to
simplify the problem by breaking a whole life into parts and
apprehending their value, and then calculating the probability of
their contributing to a good life as a whole, also leaves room for
error.



The value of an object consists in its potentiality for conducing to
intrinsically valuable experiences, and is thus a real connection
between objects, persons, and the character of experience, which we
can be empirically warranted in accepting on the basis of the
empirical evidence and the probability on the evidence of such objects
yielding such intrinsically valuable experiences. For Lewis (1946,
432), therefore, no object has intrinsic value. Nonetheless, objects
can have *inherent* value in so far as the good which they
produce is disclosable in the presence or observation of the object
itself rather than some other object. Lewis (1946, Ch. 14) contrasted
aesthetic value with cognitive and moral value, not by virtue of
distinctive characters of their felt goods, but chiefly by distinctive
attitudes to experience. The aesthetic attitude is one of
disinterested interest in the presented, attentiveness to the given in
its own right, as opposed to the cognitive attitude's concern
with prediction and significance for future experience, and the
concern on the part of the attitude of action or morality with the
pursuit of absent but attainable goods. Thanks to these differences,
aesthetic values in experience tend to be of high degree and long
lasting and don't require exclusive possession, and aesthetic
values in objects are inherent ones.



Lewis recognized that potentialities are in various ways relative to
particular circumstances and manners of observation. There is thus a
plurality of judgements of the value of objects, of the various ways
in which they can contribute and fail to contribute to intrinsically
valuable experiences, and an apparent contradictory nature to
incomplete verbal statements of them (e.g., "\(X\) is
good", "\(X\) isn't good"). For Lewis
(1946, 528), issues about the relativity or subjectivity of judgements
of the value of objects aren't issues about the empirical truth
of attributions of value to objects, but just issues about whether the
conditions under which an object produces directly apprehended value
are peculiar to the nature and capacities of a particular person and
thus not indicative of the possibility of similar value finding on the
part of other persons. Quine (1981) argued that variation within and
among individuals and societies, and the variable and open ended
character of what they find valuable, means that predicates like
"pleases" or " feels good" don't support
inductive inferences from case to case in the way that
"green" or "conducts electricity" do.
Skepticism concerning the prospects for empirical content and
empirical truth of attributions of value to objects is thus in order.
Lewis (1946, 323), on the other hand, seems to have thought that this
contention implies that no one could ever act with empirical warrant
to improve his own lot in life or do others any good, an absurdity in
his view. Lewis argued at length for the possibility of empirically
warranted judgements of the social or impersonal value of objects. The
key is that "value to more than one person is to be assessed as
if their several experiences were to be included in that of a single
person" (Lewis (1946, 550). Rawls (1971, 188-90)
criticized Lewis for mistaking impersonality for impartiality, and
denied the relevance of Lewis' account of impersonal value for
questions of justice, at least, for which impartiality is key. 



An action, for Lewis (1955, 49), is subjectively right, and one we are
not to be blamed for doing, if we think it objectively right. An
action is objectively right if it is correctly judged on the evidence
that its consequences are such as it will be right to bring about.
That requires that their pursuit violates no *categorical*
rational imperative or principle.



Lewis (1952b, 1952c, 1955, Chapter 5) outlines categorical rational
imperatives of doing and thinking, or versions of one rational
imperative, in various ways, formulations, and detail. The general
idea is laid out briefly in AKV (Lewis (1946, 480-82). To be
subject to imperatives is to find a constraint of action or thought in
what is not immediate. To be rational is to be capable of constraint
by prevision of some future good or ill, and subjection to imperatives
is simply a feature of living in human terms. Rationality turns on
consistency, and the logical is derivative from the rational. Indeed,
consistency of thought is for the sake of and aimed at consistency in
action, which in turn derives from consistency in willing, i.e., of
purposing and setting a value on. Logical consistency turns on nowhere
repudiating that to which we anywhere commit ourselves to in our
thought, and consistency in general consists in not accepting now what
we are unwilling to commit to elsewhere or later. Consistency in what
we think and do requires and is required by conformity to
*principles.* 



So there is a *categorical* rational imperative of consistency,
" Be consistent in valuation and in thought and action"
(Lewis 1946, 481) the basis of which is simply a datum of human
nature, and a broader imperative of cogency or basing one's
beliefs on cogent reasoning from evidence (Lewis 1952b, 1952c), an
imperative of prudence, "Be concerned about yourself in future
and on the whole", and an imperative of justice, "No rule
of action is right except one which is right in all instances and
therefore right for everyone" (Lewis 1946, 481-2). These
principles are simply *a priori* explications of the rational
or moral sense possessed by most humans. Certainly, this might be
challenged. In any case, Lewis thinks that where that sense is
lacking, argument for the principles is pointless, and he concludes
AKV by claiming that "valuation is always a matter of empirical
knowledge" but "what is right and what is just can never
be determined by empirical facts alone" (Lewis 1946, 554).



The problem remains of reconciling the imperatives of prudence and
(social) justice in practice, of reconciling the good for oneself with
the good for others in our self-directed, principled, thinking and
doing. What aids us is that, through language and civilization, humans
remember as a species and not merely as individuals. What we are
justified in thinking thereby is that human achievement and social
progress require autonomous, self-criticizing and self-governing
individuals, and that individual achievement and realization of
cherished goods requires membership in a social order of individuals
co-operating in the pursuit of values cherished in common. The
contrast between individual prudence and social justice seems
fundamental, Lewis concludes, perhaps rather optimistically, only by
forgetting this (Lewis 1952b).