## 1. Introduction



The dispute between rationalism and empiricism takes place primarily
within epistemology, the branch of philosophy devoted to studying the
nature, sources, and limits of knowledge. Knowledge itself can be of
many different things and is usually divided among three main
categories: knowledge of the external world, knowledge of the internal
world or self-knowledge, and knowledge of moral and/or aesthetical
values. We may find that there are category-specific conditions that
must be satisfied for knowledge to occur and that it is easier or more
difficult to shape certain questions and answers, depending on whether
we focus on the external world or on the values. However, some of the
defining questions of general epistemology include the following.


1. What is the nature of propositional knowledge, knowledge that a
particular proposition about the world, ourselves, morality, or beauty
is true?



To know a proposition, we must believe it and it must be true, but
something more is required, something that distinguishes knowledge
from a lucky guess. Let's call this additional element
'warrant'. A good deal of philosophical work has been
invested in trying to determine the nature of warrant.
2. How can we gain knowledge?



We can form true beliefs just by making lucky guesses. How to gain
warranted beliefs is less clear. Moreover, to know the external world
or anything about beauty, for instance, we must be able to think about
the external world or about beauty, and it is unclear how we gain the
concepts we use in thought or what assurance, if any, we have that the
ways in which we divide up the world using our concepts correspond to
divisions that actually exist.
3. What are the limits of our knowledge?



Some aspects of the external world, ourselves, or the moral and
aesthetical values may be within the limits of our thought but beyond
the limits of our knowledge; faced with competing descriptions of
them, we cannot know which description is true. Some aspects of the
external world, ourselves, or the moral and aesthetical values may
even be beyond the limits of our thought, so that we cannot form
intelligible descriptions of them, let alone know that a particular
description is true.



The disagreement between rationalism and empiricism primarily concerns
the second question, regarding the sources of our concepts and
knowledge. In some instances, the disagreement on this topic results
in conflicting responses to the other questions as well. The
disagreement may extend to incorporate the nature of warrant or where
the limits of our thought and knowledge are. Our focus here will be on
the competing rationalist and empiricist responses to the second
question.



There are three main theses that are usually seen as relevant for
drawing the distinction between rationalism and empiricism, with a
focus on the second question. While the first thesis has been
traditionally seen as distinguishing between rationalism and
empiricism, scholars now mostly agree that most rationalists and
empiricists abide by the so-called *Intuition/Deduction
thesis*, concerning the ways in which we become warranted in
believing propositions in a particular subject area.



> 
> *The Intuition/Deduction Thesis*: Some propositions in a
> particular subject area, S, are knowable by us by intuition alone;
> still others are knowable by being deduced from intuited propositions.
> 



Intuition is a form of direct, immediate insight. Intuition has been
likened to (a sort of internal) perception by most rationalists and
empiricists alike. Intellectually grasping a proposition, we just
"see" it to be true in such a way as to form a true,
warranted belief in it. (As discussed in Section 2 below, the nature
of this intellectual "seeing" needs explanation.)
Deduction is a process in which we derive conclusions from intuited
premises through valid arguments, ones in which the conclusion must be
true if the premises are true. We intuit, for example, that the number
three is prime and that it is greater than two. We then deduce from
this knowledge that there is a prime number greater than two.
Intuition and deduction thus provide us with knowledge that is
independent, for its justification, of experience. This type of
knowledge, since Kant, is commonly called "*a
priori*".



We can generate different versions of the Intuition/Deduction thesis
by substituting different subject areas for the variable
'S'. Several rationalists and empiricists take mathematics
to be knowable by intuition and deduction. Some place ethical truths
in this category. Some include metaphysical claims, such as that God
exists, we have free will, and our mind and body are distinct
substances.



The second thesis that is relevant to the distinction between
rationalism and empiricism is *the Innate Knowledge
thesis*.



> 
> *The Innate Knowledge Thesis*: We have knowledge of some truths
> in a particular subject area, S, as part of our nature.
> 



The Innate Knowledge thesis asserts the existence of knowledge whose
source is our own nature: we are born with this knowledge; it
doesn't depend, for its justification, on our accessing it via
particular experiences. Our innate knowledge is not learned through
either experience or intuition/deduction. It is just part of our
nature. Experiences may trigger a process by which we bring this
knowledge to consciousness, but these experiences do not provide us
with the knowledge itself. It has in some way been with us all along.
According to some rationalists, we gained the knowledge in an earlier
existence. According to others, God provided us with it at creation.
Still others say it is part of our nature through natural
selection.



We get different versions of the Innate Knowledge thesis by
substituting different subject areas for the variable 'S'.
The more subjects included within the range of the thesis or the more
controversial the claim to have knowledge in them, the more radical
the form of rationalism. Stronger and weaker understandings of warrant
yield stronger and weaker versions of the thesis as well. Empiricists
reject this thesis: Locke, for instance, dedicates the whole first
book of the *Essay* to show that such knowledge, even if it
existed, would be of little use to us.



The third important thesis that is relevant to the distinction between
rationalism and empiricism is *the Innate Concept thesis.*



> 
> *The Innate Concept Thesis*: We have some of the concepts we
> employ in a particular subject area, S, as part of our rational
> nature.
> 



According to the Innate Concept thesis, some of our concepts are not
gained from experience. They are part of our rational nature in such a
way that, while sense experiences may trigger a process by which they
are brought to consciousness, experience does not provide the concepts
or determine the information they contain. Some claim that the Innate
Concept thesis is entailed by the Innate Knowledge Thesis; a
particular instance of knowledge can only be innate if the concepts
that are contained in the known proposition are also innate. This is
Locke's position (*Essay*, 1.4.1). Others, such as
Carruthers, argue against this connection (1992, pp. 53-54). The
content and strength of the Innate Concept thesis varies with the
concepts claimed to be innate. The more a concept seems removed from
experience and the mental operations we can perform on experience the
more plausibly it may be claimed to be innate. Since we do not
experience perfect triangles but do experience pains, our concept of
the former is a more promising candidate for being innate than our
concept of the latter.


### 1.1 Rationalism



The Intuition/Deduction thesis, the Innate Knowledge thesis, and the
Innate Concept thesis are essential to rationalism. Since the
Intuition/Deduction thesis is equally important to empiricism, the
focus in what follows will be on the other two theses. To be a
rationalist is to adopt at least one of them: either the Innate
Knowledge thesis, regarding our presumed propositional innate
knowledge, or the Innate Concept thesis, regarding our supposed innate
knowledge of concepts.



Rationalists vary the strength of their view by adjusting their
understanding of warrant. Some take warranted beliefs to be beyond
even the slightest doubt and claim that intuition provide beliefs of
this high epistemic status. Others interpret warrant more
conservatively, say as belief beyond a reasonable doubt, and claim
that intuition provide beliefs of that caliber. Still another
dimension of rationalism depends on how its proponents understand the
connection between intuition, on the one hand, and truth, on the
other. Some take intuition to be infallible, claiming that whatever we
intuit must be true. Others allow for the possibility of false
intuited propositions.



Two other closely related theses are generally adopted by
rationalists, although one can certainly be a rationalist without
adopting either of them. The first is that sense experience cannot
provide what we gain from reason.



> 
> *The Indispensability of Reason Thesis*: The knowledge we gain
> in subject area, S, by intuition and deduction, as well as the ideas
> and instances of knowledge in S that are innate to us, could not have
> been gained by us through sense experience.
> 



The second is that reason is superior to sense experience as a source
of knowledge.



> 
> *The Superiority of Reason Thesis*: The knowledge we gain in
> subject area S by intuition and deduction or have innately is superior
> to any knowledge gained by sense experience.
> 



How reason is superior needs explanation, and rationalists have
offered different accounts. One view, generally associated with
Descartes (*Rules,* Rule II and Rule III, pp. 1-4), is
that what we know *by intuition* is certain, beyond even the
slightest doubt, while what we believe, or even know, on the basis of
sense experience is at least somewhat uncertain. Another view,
generally associated with Plato (*Republic* 479e-484c), locates
the superiority of *a priori* knowledge in the objects known.
What we know by reason alone, a Platonic form, say, is superior in an
important metaphysical way, e.g. unchanging, eternal, perfect, a
higher degree of being, to what we are aware of through sense
experience.



Most forms of rationalism involve notable commitments to other
philosophical positions. One is a commitment to the denial of
scepticism for at least some area of knowledge. If we claim to know
some truths by intuition or deduction or to have some innate
knowledge, we obviously reject scepticism with regard to those truths.
Rationalism in the form of the Intuition/Deduction thesis is also
committed to epistemic foundationalism, the view that we know some
truths without basing our belief in them on any others and that we
then use this foundational knowledge to know more truths.


### 1.2 Empiricism



Empiricists also endorse the Intuition/Deduction thesis, but in a more
restricted sense than the rationalists: this thesis applies only to
relations of the contents of our minds, not also about empirical
facts, learned from the external world. By contrast, empiricists
reject the Innate Knowledge and Innate Concept theses. Insofar as we
have knowledge in a subject, our knowledge is *gained*, not
only triggered, by our experiences, be they sensorial or
reflective. Experience is, thus, our only source of ideas. Moreover,
they reject the corresponding version of the Superiority of Reason
thesis. Since reason alone does not give us any knowledge, it
certainly does not give us superior knowledge. Empiricists need not
reject the Indispensability of Reason thesis, but most of them do.



The main characteristic of empiricism, however, is that it endorses a
version of the following claim for some subject area:



> 
> *The Empiricism Thesis*: We have no source of knowledge in S or
> for the concepts we use in S other than experience.
> 



To be clear, the Empiricism thesis does not entail that we have
empirical knowledge. It entails that knowledge can only be gained,
*if at all*, by experience. Empiricists may assert, as some do
for some subjects, that the rationalists are correct to claim that
experience cannot give us knowledge. The conclusion they draw from
this rationalist lesson is that we do not know at all. This is,
indeed, Hume's position with regard to causation, which, he argues, is
not actually known, but only presupposed to be holding true, in virtue
of a particular habit of our minds.



We have stated the basic claims of rationalism and empiricism so that
each is relative to a particular subject area. Rationalism and
empiricism, so relativized, need not conflict. We can be rationalists
in mathematics or a particular area of mathematics and empiricists in
all or some of the physical sciences. Rationalism and empiricism only
conflict when formulated to cover the same subject. Then the debate,
Rationalism vs. Empiricism, is joined. The fact that philosophers can
be both rationalists and empiricists has implications for the
classification schemes often employed in the history of philosophy,
especially the one traditionally used to describe the Early Modern
Period of the seventeenth and eighteenth centuries leading up to Kant.
It is standard practice to group the philosophers of this period as
either rationalists or empiricists and to suggest that those under one
heading share a common agenda in opposition to those under the other.
Thus, Descartes, Spinoza and Leibniz are the Continental Rationalists
in opposition to Locke, Hume, and Reid, the British Empiricists. Such
general classification schemes should only be adopted with great
caution. The views of the individual philosophers are a lot more
subtle and complex than the simple-minded classification suggests.
(See Loeb (1981) and Kenny (1986) for important discussions of this
point.) Locke rejects rationalism in the form of any version of the
Innate Knowledge or Innate Concept theses, but he nonetheless adopts
the Intuition/Deduction thesis with regard to our knowledge of
God's existence, in addition to our knowledge of mathematics and
morality. Descartes and Locke have remarkably similar views on the
nature of our ideas, even though Descartes takes many to be innate,
while Locke ties them all to experience. The rationalist/empiricist
classification also encourages us to expect the philosophers on each
side of the divide to have common research programs in areas beyond
epistemology. Thus, Descartes, Spinoza and Leibniz are mistakenly seen
as applying a reason-centered epistemology to a common metaphysical
agenda, with each trying to improve on the efforts of the one before,
while Locke, Hume, and Reid are mistakenly seen as gradually rejecting
those metaphysical claims, with each consciously trying to improve on
the efforts of his predecessors. It is also important to note that the
rationalist/empiricist distinction is not exhaustive of the possible
sources of knowledge. One might claim, for example, that we can gain
knowledge in a particular area by a form of Divine revelation or
insight that is a product of neither reason nor sense experience. In
short, when used carelessly, the labels 'rationalist' and
'empiricist,' as well as the slogan that is the title of
this essay, 'Rationalism vs. Empiricism,' can impede
rather than advance our understanding.



An important wrinkle for using this classification scheme in the
history of philosophy is that it leaves out discussions of
philosophical figures who did not focus their efforts on understanding
whether innate knowledge is possible or even fruitful to have.
Philosophy in the early modern period, in particular, is a lot richer
than this artificial, simplifying distinction makes it sound. There is
no clear way of grouping Hobbes with either camp, let alone Elizabeth
of Bohemia, Anne Conway, George Berkeley, Emilie du
Chatelet, or Mary Shepherd. This distinction, initially applied
by Kant, is responsible for giving us a very restrictive philosophical
canon, which does not take into account developments in the philosophy
of emotions, philosophy of education, and even disputes in areas of
philosophy considered more mainstream, like ethics and aesthetics.



Unless restricted to debates regarding the possibility of innate
knowledge, this distinction is best left unused. The most interesting
form of the debate occurs when we take the relevant subject to be
truths about the external world, the world beyond our own minds. A
full-fledged rationalist with regard to our knowledge of the external
world holds that some external world truths are and must be innate and
that this knowledge is superior to any that sense experience could
ever provide. The full-fledged empiricist about our knowledge of the
external world replies that, when it comes to the nature of the world
beyond our own minds, experience is our sole source of information.
Reason might inform us of the relations among our ideas, but those
ideas themselves can only be gained, and any truths about the external
reality they represent can only be known, on the basis of experience.
This debate concerning our knowledge of the external world will
generally be our main focus in what follows.



Historically, the rationalist/empiricist dispute in epistemology has
extended into the area of metaphysics, where philosophers are
concerned with the basic nature of reality, including the existence of
God and such aspects of our nature as free-will and the relation
between the mind and body. Several rationalists (e.g., Descartes,
*Meditations*) have presented metaphysical theories, which they
have claimed to know by intuition and/or deduction alone. Empiricists
(e.g., Hume, *Treatise)* have rejected the theories as either
speculation, beyond what we can learn from experience, or nonsensical
attempts to describe aspects of the world beyond the concepts
experience can provide. The debate raises the issue of metaphysics as
an area of knowledge. Kant puts the driving assumption clearly:



> 
> The very concept of metaphysics ensures that the sources of
> metaphysics can't be empirical. If something could be known
> through the senses, that would automatically show that it
> doesn't belong to metaphysics; that's an upshot of the
> meaning of the word 'metaphysics.' Its basic principles
> can never be taken from experience, nor can its basic concepts; for it
> is not to be physical but metaphysical knowledge, so it must be beyond
> experience. (*Prolegomena*, Preamble, I, p. 7)
> 



The possibility then of metaphysics so understood, as an area of human
knowledge, hinges on how we resolve the rationalist/empiricist debate.
The debate also extends into ethics. Some moral objectivists (e.g.,
Ross 1930 and Huemer 2005) take us to know some fundamental objective
moral truths by intuition, while some moral skeptics, who reject such
knowledge (e.g., Mackie 1977), find the appeal to a faculty of moral
intuition utterly implausible. More recently, the
rationalist/empiricist debate has extended to discussions (e.g.,
Bealer 1999 and Alexander & Weinberg 2007) of the very nature of
philosophical inquiry: to what extent are philosophical questions to
be answered by appeals to reason or experience?


## 2. The Intuition/Deduction Thesis



The Intuition/Deduction thesis claims that we can know some
propositions by intuition and still more by deduction. Since
traditionally this thesis was thought to be rejected by empiricists
and adopted only by rationalists, it is useful to become more familiar
with it. In a very narrow sense, only rationalists seem to adopt it.
However, the current consensus is that most empiricists (e.g., Locke,
Hume, Reid) have been willing to accept a version of the thesis,
namely inasmuch as it is restricted to propositions solely about the
relations among our own concepts. We can, they agree, know by
intuition that our concept of God includes our concept of omniscience.
Just by examining the concepts, we can intellectually grasp that the
one includes the other. The debate between rationalists and
empiricists is joined when the former assert, and the latter deny, the
Intuition/Deduction thesis with regard to propositions that contain
substantive information about the external world. Rationalists, such
as Descartes, have claimed that we can know by intuition and deduction
that God exists and created the world, that our mind and body are
distinct substances, and that the angles of a triangle equal two right
angles, where all of these claims are truths about an external reality
independent of our thought. Such substantive versions of the
Intuition/Deduction thesis are our concern in this section.



One defense of the Intuition/Deduction thesis assumes that we know
some substantive external world truths, adds an analysis of what
knowledge requires, and concludes that our knowledge must result from
intuition and deduction. Rationalists and empiricists alike claim that
certainty is required for *scientia* (which is a type of
absolute knowledge of the necessary connections that would explain why
certain things are a certain way) and that certainty about the
external world is beyond what empirical evidence can provide.
Empiricists seem happy to then conclude that the type of knowledge of
the external world that we can acquire does not have this high degree
of certainty and is, thus, not *scientia*. This is because we
can never be sure our sensory impressions are not part of a dream or a
massive, demon orchestrated, deception. A rationalist like Descartes
of the *Meditations*, claims that only intuition can provide
the certainty needed for such knowledge. This, after his arguing in
the *Rules* that, when we "review all the actions of the
intellect by means of which we are able to arrive at a knowledge of
things with no fear of being mistaken," we "recognize only
two: intuition and deduction" (*Rules*, Rule III,
p. 3).



This line of argument is one of the least compelling in the
rationalist arsenal. First, the assumption that knowledge requires
certainty comes at a heavy cost, as it rules out so much of what we
commonly take ourselves to know. Second, as many contemporary
rationalists accept, intuition is not always a source of certain
knowledge. The possibility of a deceiver gives us a reason to doubt
our intuitions as well as our empirical beliefs. For all we know, a
deceiver might cause us to intuit false propositions, just as one
might cause us to have perceptions of nonexistent objects.
Descartes's classic way of meeting this challenge in the
*Meditations* is to argue that we can know with certainty that
no such deceiver interferes with our intuitions and deductions. They
are infallible, as God guarantees their truth. The problem, known as
the Cartesian Circle, is that Descartes's account of how we gain
this knowledge begs the question, by attempting to deduce the
conclusion that all our intuitions are true from intuited premises.
Moreover, his account does not touch a remaining problem that he
himself notes (*Rules*, Rule VII, p. 7): Deductions of any
appreciable length rely on our fallible memory.



A more plausible argument for the Intuition/Deduction thesis again
assumes that we know some particular, external world truths, and then
appeals to the nature of what we know, rather than to the nature of
knowledge itself, to argue that our knowledge must result from
intuition and deduction. Leibniz, in *New Essays*, tells us the
following:



> 
> The senses, although they are necessary for all our actual knowledge,
> are not sufficient to give us the whole of it, since the senses never
> give anything but instances, that is to say particular or individual
> truths. Now all the instances which confirm a general truth, however
> numerous they may be, are not sufficient to establish the universal
> necessity of this same truth, for it does not follow that what
> happened before will happen in the same way again. ... From which
> it appears that necessary truths, such as we find in pure mathematics,
> and particularly in arithmetic and geometry, must have principles
> whose proof does not depend on instances, nor consequently on the
> testimony of the senses, although without the senses it would never
> have occurred to us to think of them... (*New Essays*,
> Preface, pp. 150-151)
> 



Leibniz goes on to describe our mathematical knowledge as
"innate," and his argument is more commonly directed to
support the Innate Knowledge thesis rather than the
Intuition/Deduction thesis. For our purposes here, we can relate it to
the latter, however: We have substantive knowledge about the external
world in mathematics, and what we know in that area, we know to be
necessarily true. Experience cannot warrant beliefs about what is
necessarily the case. Hence, experience cannot be the source of our
knowledge. The best explanation of our knowledge is that we gain it by
intuition and deduction. Leibniz mentions logic, metaphysics, and
morals as other areas in which our knowledge similarly outstrips what
experience can provide. Judgments in logic and metaphysics involve
forms of necessity beyond what experience can support. Judgments in
morals involve a form of obligation or value that lies beyond
experience, which only informs us about what is the case rather than
about what ought to be.



The strength of this argument varies with its examples of purported
knowledge. Insofar as we focus on controversial claims in metaphysics,
e.g., that God exists, that our mind is a distinct substance from our
body, the initial premise that we know the claims is less than
compelling. Taken with regard to other areas, however, the argument
clearly has legs. We know a great deal of mathematics, and what we
know, we know to be necessarily true. None of our experiences warrants
a belief in such necessity, and we do not seem to base our knowledge
on any experiences. The warrant that provides us with knowledge arises
from an intellectual grasp of the propositions which is clearly part
of our learning. Similarly, we seem to have such moral knowledge as
that, all other things being equal, it is wrong to break a promise and
that pleasure is intrinsically good. No empirical lesson about how
things are can warrant such knowledge of how they ought to be.



This argument for the Intuition/Deduction thesis raises additional
questions which rationalists must answer. Insofar as they maintain
that our knowledge of necessary truths in mathematics or elsewhere by
intuition and deduction is substantive knowledge of the external
world, they owe us an account of this form of necessity. Many
empiricists stand ready to argue that "necessity resides in the
way we talk about things, not in the things we talk about"
(Quine 1966, p. 174). Similarly, if rationalists claim that our
knowledge in morals is knowledge of an objective form of obligation,
they owe us an account of how objective values are part of a world of
apparently valueless facts.



Perhaps most of all, any defenders of the Intuition/Deduction thesis
owe us an account of what intuition is and how it provides warranted
true beliefs about the external world. What is it to intuit a
proposition and how does that act of intuition support a warranted
belief? Their argument presents intuition and deduction as an
explanation of assumed knowledge that can't--they
say--be explained by experience, but such an explanation by
intuition and deduction requires that we have a clear understanding of
intuition and how it supports warranted beliefs. Metaphorical
characterizations of intuition as intellectual "grasping"
or "seeing" are not enough, and if intuition is some form
of intellectual "grasping," it appears that all that is
grasped is relations among our concepts, rather than facts about the
external world, as the empiricists defenders of intuition and
deduction argue. One current approach to the issue involves an appeal
to Phenomenal Conservatism (Huemer 2001), the principle that if it
seems to one as if something is the case, then one is prima facie
justified in believing that it is so. Intuitions are then taken to be
a particular sort of seeming or appearance: "[A]n intuition that
p is a state of its seeming to one that p that is not dependent on
inference from other beliefs and that results from thinking about p,
as opposed to perceiving, remembering, or introspecting" (Huemer
2005, p. 102). Just as it can visually seem or appear to one as if
there's a tree outside the window, it can intellectually seem or
appear to one as if nothing can be both entirely red and entirely
green. This approach aims to demystify intuitions; they are but one
more form of seeming-state along with ones we gain from sense
perception, memory, and introspection. It does not, however, tell us
all we need to know. Any intellectual faculty, whether it be sense
perception, memory, introspection or intuition, provides us with
warranted beliefs only if it is generally reliable. The reliability of
sense perception stems from the causal connection between how external
objects are and how we experience them. What accounts for the
reliability of our intuitions regarding the external world? Is our
intuition of a particular true proposition the outcome of some causal
interaction between ourselves and some aspect of the world? What
aspect? What is the nature of this causal interaction? That the number
three is prime does not appear to cause anything, let alone our
intuition that it is prime. As Michael Huemer (2005, p. 123) points
out in mounting his own defense of moral intuitionism, "The
challenge for the moral realist, then, is to explain how it would be
anything more than chance if my moral beliefs were true, given that I
do not interact with moral properties."



These issues are made all the more pressing by the classic empiricist
response to the argument. The reply is generally credited to Hume and
begins with a division of all true propositions into two
categories.



> 
> All the objects of human reason or inquiry may naturally be divided
> into two kinds, to wit, "Relations of Ideas," and
> "Matters of Fact." Of the first are the sciences of
> Geometry, Algebra, and Arithmetic, and, in short, every affirmation
> which is either intuitively or demonstratively certain. That the
> square of the hypotenuse is equal to the square of the two sides is a
> proposition which expresses a relation between these figures. That
> three times five is equal to half of thirty expresses a relation
> between these numbers. Propositions of this kind are discoverable by
> the mere operation of thought, without dependence on what is anywhere
> existent in the universe. Though there never were a circle or triangle
> in nature, the truths demonstrated by Euclid would forever retain
> their certainty and evidence. Matters of fact, which are the second
> objects of human reason, are not ascertained in the same manner, nor
> is our evidence of their truth, however great, of a like nature with
> the foregoing. The contrary of every matter of fact is still possible,
> because it can never imply a contradiction and is conceived by the
> mind with the same facility and distinctness as if ever so conformable
> to reality. (*Enquiry*, 4.1, p. 24)
> 



Intuition and deduction can provide us with knowledge of necessary
truths such as those found in mathematics and logic, but such
knowledge is not substantive knowledge of the external world. It is
only knowledge of the relations of our own ideas. If the rationalist
shifts the argument so it appeals to knowledge in morals, Hume's
reply is to offer an analysis of our moral concepts by which such
knowledge is empirically gained knowledge of matters of fact.



> 
> Morals and criticism are not so properly objects of the understanding
> as of taste and sentiment. Beauty, whether moral or natural, is felt
> more properly than perceived. Or if we reason concerning it and
> endeavor to fix the standard, we regard a new fact, to wit, the
> general taste of mankind, or some other fact which may be the object
> of reasoning and inquiry. (*Enquiry*, 12.3, p. 122)
> 



If the rationalist appeals to our knowledge in metaphysics to support
the argument, Hume denies that we have such knowledge.



> 
> If we take in our hand any volume--of divinity or school metaphysics,
> for instance--let us ask, Does it contain any abstract reasoning
> concerning quantity or number? No. Does it contain any experimental
> reasoning concerning matter of fact and existence? No. Commit it then
> to the flames, for it can contain nothing but sophistry and illusion.
> (*Enquiry*, 12.3, p. 123)
> 



An updated version of this general empiricist reply, with an increased
emphasis on language and the nature of meaning, is given in the
twentieth-century by A. J. Ayer's version of logical positivism.
Adopting positivism's verification theory of meaning, Ayer
assigns every cognitively meaningful sentence to one of two
categories: either it is a tautology, and so true solely by virtue of
the meaning of its terms and provides no substantive information about
the world, or it is open to empirical verification. There is, then, no
room for knowledge about the external world by intuition or
deduction.



> 
> There can be no *a priori* knowledge of reality. For ...
> the truths of pure reason, the propositions which we know to be valid
> independently of all experience, are so only in virtue of their lack
> of factual content ... [By contrast] empirical propositions are
> one and all hypotheses which may be confirmed or discredited in actual
> sense experience. (Ayer 1952, pp. 86; 93-94)
> 



The rationalists' argument for the Intuition/Deduction thesis
goes wrong at the start, according to empiricists, by assuming that we
can have substantive knowledge of the external world that outstrips
what experience can warrant. We cannot.



This empiricist reply faces challenges of its own. Our knowledge of
mathematics seems to be about something more than our own concepts.
Our knowledge of moral judgments seems to concern not just how we feel
or act but how we ought to behave. The general principles that provide
a basis for the empiricist view, e.g. Hume's overall account of
our ideas, the Verification Principle of Meaning, are problematic in
their own right.



In all, rationalists have an argument for the Intuition/Deduction
thesis relative to our substantive knowledge of the external world,
but its success rests on how well they can answer questions about the
nature and epistemic force of intuition made all the more pressing by
the classic empiricist reply.


## 3. The Innate Knowledge Thesis



The Innate Knowledge thesis asserts that we have *a priori*
knowledge, that is knowledge independent, for its justification, of
sense experience, as part of our rational nature. Experience may
trigger our awareness of this knowledge, but it does not provide us
with it. The knowledge is already there.



Plato presents an early version of the Innate Knowledge thesis in the
*Meno* as the doctrine of knowledge by recollection. The
doctrine is motivated in part by a paradox that arises when we attempt
to explain the nature of inquiry. How do we gain knowledge of a
theorem in geometry? We inquire into the matter. Yet, knowledge by
inquiry seems impossible (*Meno*, 80d-e). We either already
know the theorem at the start of our investigation or we do not. If we
already have the knowledge, there is no place for inquiry. If we lack
the knowledge, we don't know what we are seeking and cannot
recognize it when we find it. Either way we cannot gain knowledge of
the theorem by inquiry. Yet, we do know some theorems.



The doctrine of knowledge by recollection offers a solution. When we
inquire into the truth of a theorem, we both do and do not already
know it. We have knowledge in the form of a memory gained from our
soul's knowledge of the theorem prior to its union with our
body. We also lack some knowledge because, in our soul's
unification with the body, it has forgotten the knowledge and now
needs to recollect it. Thus, learning the theorem allows us, in
effect, to recall what we already know.



Plato famously illustrates the doctrine with an exchange between
Socrates and a young slave, in which Socrates guides the slave from
ignorance to mathematical knowledge. The slave's experiences, in
the form of Socrates' questions and illustrations, are the
occasion for his recollection of what he learned previously.
Plato's metaphysics provides additional support for the Innate
Knowledge Thesis. Since our knowledge is of abstract, eternal Forms,
which clearly lie beyond our sensory experience, it is independent,
for its justification, of experience.



Contemporary supporters of Plato's position are scarce. The
initial paradox, which Plato describes as a "trick
argument" (*Meno*, 80e), rings sophistical. The
metaphysical assumptions in the solution need justification. The
solution does not answer the basic question: Just how did the
slave's soul learn the theorem? The Intuition/Deduction thesis
offers an equally, if not more, plausible account of how the slave
gains this type of knowledge that is independent of experience.
Nonetheless, Plato's position illustrates the kind of reasoning
that has caused many philosophers to adopt some form of the Innate
Knowledge thesis. We are confident that we know certain propositions
about the external world, but there seems to be no adequate
explanation of how we gained this knowledge short of saying that it is
innate. Its content is beyond what we directly gain in experience, as
well as what we can gain by performing mental operations on what
experience provides. It does not seem to be based on an intuition or
deduction. That it is innate in us appears to be the best
explanation.



Noam Chomsky argues along similar lines in presenting what he
describes as a "rationalist conception of the nature of
language" (1975, p. 129). Chomsky argues that the experiences
available to language learners are far too sparse to account for their
knowledge of their language. To explain language acquisition, we must
assume that learners have an innate knowledge of a universal grammar
capturing the common deep structure of natural languages. It is
important to note that Chomsky's language learners do not know
particular propositions describing a universal grammar. They have a
set of innate capacities or dispositions which enable and determine
their language development. Chomsky gives us a theory of innate
learning capacities or structures rather than a theory of innate
knowledge. His view does not support the Innate Knowledge thesis as
rationalists have traditionally understood it. As one commentator puts
it, "Chomsky's principles ... are innate neither in
the sense that we are explicitly aware of them, nor in the sense that
we have a disposition to recognize their truth as obvious under
appropriate circumstances. And hence it is by no means clear that
Chomsky is correct in seeing his theory as following the traditional
rationalist account of the acquisition of knowledge" (Cottingham
1984, p. 124). Indeed, such a theory, which places nativism at the
level of mental capacities or structures enabling us to acquire
certain types of knowledge rather than at the level of knowledge we
already posses, is akin to an empiricist take on the issue. Locke and
Reid, for instance, believe that the human mind is endowed with
certain abilities that, when developed in the usual course of nature,
will lead us to acquire useful knowledge of the external world. The
main idea is that it is part of our biology to have a digestive system
that, when fed the right kind of food, allows us to process the
required nutrients to enable us to continue to live for a while.
Similarly, it is part of our biology to have a mental architecture
that, when fed the right kind of information and experiences, allows
us to process that information and transform it into knowledge. The
knowledge itself is no more innate than the processed nutrients are.
On a view like this, no knowledge is innate; however, we are born with
certain capabilities and disposition that enable us to acquire
knowledge, just as we are equipped with certain organs that allow our
bodies to function well while we're alive.



Peter Carruthers (1992) argues that we have innate knowledge of the
principles of folk-psychology. Folk-psychology is a network of
common-sense generalizations that hold independently of context or
culture and concern the relationships of mental states to one another,
to the environment and states of the body and to behavior (1992, p.
115). It includes such beliefs as that pains tend to be caused by
injury, that pains tend to prevent us from concentrating on tasks, and
that perceptions are generally caused by the appropriate state of the
environment. Carruthers notes the complexity of folk-psychology, along
with its success in explaining our behavior and the fact that its
explanations appeal to such unobservables as beliefs, desires,
feelings, and thoughts. He argues that the complexity, universality,
and depth of folk-psychological principles outstrips what experience
can provide, especially to young children who by their fifth year
already know a great many of them. This knowledge is also not the
result of intuition or deduction; folk-psychological generalizations
are not seen to be true in an act of intellectual insight. Carruthers
concludes, "[The problem] concerning the child's
acquisition of psychological generalizations cannot be solved, unless
we suppose that much of folk-psychology is already innate, triggered
locally by the child's experience of itself and others, rather
than learned" (1992, p. 121).



Empiricists, and some rationalists, attack the Innate Knowledge thesis
in two main ways. First, they offer accounts of how sense experience
or intuition and deduction provide the knowledge that is claimed to be
innate. Second, they directly criticize the Innate Knowledge thesis
itself. The classic statement of this second line of attack is
presented in Locke's *Essay*. Locke raises the issue of
just what innate knowledge is. Particular instances of knowledge are
supposed to be in our minds as part of our rational make-up, but how
are they "in our minds"? If the implication is that we all
consciously have this knowledge, it is plainly false. Propositions
often given as examples of innate knowledge, even such plausible
candidates as the principle that the same thing cannot both be and not
be, are not consciously accepted by children and those with severe
cognitive limitations. If the point of calling such principles
"innate" is not to imply that they are or have been
consciously accepted by all rational beings, then it is hard to see
what the point is. "No proposition can be said to be in the
mind, which it never yet knew, which it never yet was conscious
of" (*Essay*, 1.2.5). Proponents of innate knowledge
might respond that some knowledge is innate in that we have the
capacity to have it. That claim, while true, is of little interest,
however. "If the capacity of knowing, be the natural impression
contended for, all the truths a man ever comes to know, will, by this
account, be every one of them, innate; and this great point will
amount to no more, but only an improper way of speaking; which whilst
it pretends to assert the contrary, says nothing different from those,
who deny innate principles. For nobody, I think, ever denied, that the
mind was capable of knowing several truths" (*Essay*,
1.2.5). Locke thus challenges defenders of the Innate Knowledge thesis
to present an account of innate knowledge that allows their position
to be both true and interesting. A narrow interpretation of innateness
faces counterexamples of rational individuals who do not meet its
conditions. A generous interpretation implies that all our knowledge,
even that clearly provided by experience, is innate.



Defenders of innate knowledge take up Locke's challenge. Leibniz
responds in *New Essays* by appealing to an account of
innateness in terms of natural potential to avoid Locke's
dilemma. Consider Peter Carruthers' similar reply.



> 
> We have noted that while one form of nativism claims (somewhat
> implausibly) that knowledge is innate in the sense of being present as
> such (or at least in propositional form) from birth, it might also be
> maintained that knowledge is innate in the sense of being innately
> determined to make its appearance at some stage in childhood. This
> latter thesis is surely the most plausible version of nativism. (1992,
> p. 51)
> 



Carruthers claims that our innate knowledge is determined through
evolutionary selection (p. 111). Evolution has resulted in our being
determined to know certain things (e.g. principles of folk-psychology)
at particular stages of our life, as part of our natural development.
Experiences provide the occasion for our consciously believing the
known propositions but not the basis for our knowledge of them (p.
52). Carruthers thus has a ready reply to Locke's
counterexamples of children and cognitively limited persons who do not
believe propositions claimed to be instances of innate knowledge. The
former have not yet reached the proper stage of development; the
latter are persons in whom natural development has broken down (pp.
49-50).



A serious problem for the Innate Knowledge thesis remains, however. We
know a proposition only if it is true, we believe it and our belief is
warranted. Rationalists who assert the existence of innate knowledge
are not just claiming that, as a matter of human evolution,
God's design or some other factor, at a particular point in our
development, certain sorts of experiences trigger our belief in
particular propositions in a way that does not involve our learning
them from the experiences. Their claim is even bolder: In at least
some of these cases, our empirically triggered, but not empirically
warranted, belief is nonetheless warranted and so known. How can these
beliefs be warranted if they do not gain their warrant from the
experiences that cause us to have them or from intuition and
deduction?



Some rationalists think that a reliabilist account of warrant provides
the answer. According to Reliabilism, beliefs are warranted if they
are formed by a process that generally produces true beliefs rather
than false ones. The true beliefs that constitute our innate knowledge
are warranted, then, because they are formed as the result of a
reliable belief-forming process. Carruthers maintains that
"Innate beliefs will count as known provided that the process
through which they come to be innate is a reliable one (provided, that
is, that the process tends to generate beliefs that are true)"
(1992, p. 77). He argues that natural selection results in the
formation of some beliefs and is a truth-reliable process.



An appeal to Reliabilism, or a similar causal theory of warrant, may
well be the best way to develop the Innate Knowledge thesis. Even so,
some difficulties remain. First, reliabilist accounts of warrant are
themselves quite controversial. Second, rationalists must give an
account of innate knowledge that maintains and explains the
distinction between innate knowledge and non-innate knowledge, and it
is not clear that they will be able to do so within such an account of
warrant. Suppose for the sake of argument that we have innate
knowledge of some proposition, *P*. What makes our knowledge
that *P* innate? To sharpen the question, what difference
between our knowledge that *P* and a clear case of non-innate
knowledge, say our knowledge that something is red based on our
current visual experience of a red table, makes the former innate and
the latter not innate? In each case, we have a true, warranted belief.
In each case, presumably, our belief gains its warrant from the fact
that it meets a particular causal condition, e.g., it is produced by a
reliable process. In each case, the causal process is one in which an
experience causes us to believe the proposition at hand (that
*P*; that something is red), for, as defenders of innate
knowledge admit, our belief that *P* is "triggered"
by an experience, as is our belief that something is red. The insight
behind the Innate Knowledge thesis seems to be that the difference
between our innate and non-innate knowledge lies in the relation
between our experience and our belief in each case. The experience
that causes our belief that *P* does not "contain"
the information that *P*, while our visual experience of a red
table does "contain" the information that something is
red. Yet, exactly what is the nature of this containment relation
between our experiences, on the one hand, and what we believe, on the
other, that is missing in the one case but present in the other? The
nature of the experience-belief relation seems quite similar in each.
The causal relation between the experience that triggers our belief
that *P* and our belief that *P* is contingent, as is
the fact that the belief-forming process is reliable. The same is true
of our experience of a red table and our belief that something is red.
The causal relation between the experience and our belief is again
contingent. We might have been so constructed that the experience we
describe as "being appeared to redly" caused us to
believe, not that something is red, but that something is hot. The
process that takes us from the experience to our belief is also only
contingently reliable. Moreover, if our experience of a red table
"contains" the information that something is red, then
that fact, not the existence of a reliable belief-forming process
between the two, should be the reason why the experience warrants our
belief. By appealing to Reliabilism, or some other causal theory of
warrant, rationalists may obtain a way to explain how innate knowledge
can be warranted. They still need to show how their explanation
supports an account of the difference between innate knowledge and
non-innate knowledge. So, Locke's criticism -- that there is no true
distinction between innate versus non-innate knowledge that
rationalists may draw -- still stands, in the face of the best
rationalist defense of the Innate Knowledge thesis.


## 4. The Innate Concept Thesis



According to the Innate Concept thesis, some of our concepts have not
been gained from experience. They are instead part of our rational
make-up, and experience simply triggers a process by which we
consciously grasp them. The main concern motivating the rationalist
should be familiar by now: the content of some concepts seems to
outstrip anything we could have gained from experience. An example of
this reasoning is presented by Descartes in the *Meditations*.
Although he sometimes seems committed to the view that all our ideas
are innate (Adams 1975 and Gotham 2002), he there classifies our ideas
as adventitious, invented by us, and innate. Adventitious ideas, such
as a sensation of heat, are gained directly through sense experience.
Ideas invented by us, such as our idea of a hippogriff, are created by
us from other ideas we possess. Innate ideas, such as our ideas of
God, of extended matter, of substance, and of a perfect triangle, are
placed in our minds by God at creation. Consider Descartes's
argument that our concept of God, as an infinitely perfect being, is
innate. Our concept of God is not directly gained in experience, as
particular tastes, sensations, and mental images might be. Its content
is beyond what we could ever construct by applying available mental
operations to what experience directly provides. From experience, we
can gain the concept of a being with finite amounts of various
perfections, one, for example, that is finitely knowledgeable,
powerful and good. We cannot however move from these empirical
concepts to the concept of a being of infinite perfection. ("I
must not think that, just as my conceptions of rest and darkness are
arrived at by negating movement and light, so my perception of the
infinite is arrived at not by means of a true idea but by merely
negating the finite," Third Meditation, p. 94.) Descartes
supplements this argument by another. Not only is the content of our
concept of God beyond what experience can provide, the concept is a
prerequisite for our employment of the concept of finite perfection
gained from experience. ("My perception of the infinite, that is
God, is in some way prior to my perception of the finite, that is
myself. For how could I understand that I doubted or
desired--that is lacked something--and that I was not wholly
perfect, unless there were in me some idea of a more perfect being
which enabled me to recognize my own defects by comparison,"
Third Meditation, p. 94).



An empiricist response to this general line of argument is given by
Locke (*Essay*, 1.4.1-25). First, there is the problem of
explaining what it is for someone to have an innate concept. If having
an innate concept entails consciously entertaining it at present or in
the past, then Descartes's position is open to obvious
counterexamples. Young children and people from other cultures do not
consciously entertain the concept of God and have not done so. Second,
there is the objection that we have no need to appeal to innate
concepts in the first place. Contrary to Descartes's argument,
we can explain how experience provides all our ideas, including those
the rationalists take to be innate, and with just the content that the
rationalists attribute to them.



Leibniz's *New Essays* offers a rationalist reply to the
first concern. Where Locke puts forth the image of the mind as a blank
slate on which experience writes, Leibniz offers us the image of a
block of marble, the veins of which determine what sculpted figures it
will accept (*New Essays*, Preface, p. 153). Leibniz's
metaphor contains an insight that Locke misses. The mind plays a role
in determining the nature of its contents. This point does not,
however, require the adoption of the Innate Concept thesis. Locke
might still point out that we are not required to have the concepts
themselves and the ability to use them, innately. In contemporary
terms, what we are required to have is the right hardware that allows
for the optimal running of the actual software. For Locke, there are
no constrains here; for Leibniz, only a particular type of software
is, indeed, able to be supported by the extant hardware. Put
differently, the hardware itself determines what software can be
optimally run, for a Leibnizian.



Rationalists have responded to the second part of the empiricist
attack on the Innate Concept thesis--the empiricists' claim
that the thesis is without basis, as all our ideas can be explained as
derived from experience--by focusing on difficulties in the
empiricists' attempts to give such an explanation. The
difficulties are illustrated by Locke's account. According to
Locke, experience consists in external sensation and inner reflection.
All our ideas are either simple or complex, with the former being
received by us passively in sensation or reflection and the latter
being built by the mind from simple materials through various mental
operations. Right at the start, the account of how simple ideas are
gained is open to an obvious counterexample acknowledged, but then set
aside, by Hume in presenting his own empiricist theory. Consider the
mental image of a particular shade of blue. If Locke is right, the
idea is a simple one and should be passively received by the mind
through experience. Hume points out otherwise:



> 
> Suppose therefore a person to have enjoyed his sight for thirty years
> and to have become perfectly acquainted with colors of all kinds,
> except one particular shade of blue, for instance, which it never has
> been his fortune to meet with; let all the different shades of that
> color, except that single one, be placed before him, descending
> gradually from the deepest to the lightest, it is plain that he will
> perceive a blank where that shade is wanting and will be sensible that
> there is a greater distance in that place between the contiguous
> colors than in any other. Now I ask whether it be possible for him,
> from his own imagination, to supply this deficiency and raise up to
> himself the idea of that particular shade, though it had never been
> conveyed to him by his senses? I believe there are but few will be of
> the opinion that he can... (*Enquiry*, 2, pp. 15-16)
> 



Even when it comes to such simple ideas as the image of a particular
shade of blue, the mind seems to be more than a blank slate on which
experience writes. The main question is whether the veins in
Leibniz's metaphor should count as part of the knowledge or just
as part of our biological mental architecture: all the knowledge we
can ever acquire is constrained by the type of beings we are. This does
not require our positing that concepts be part of the inner workings,
at the beginning of our lives.



On the other hand, consider, too, our concept of a particular color,
say red. Critics of Locke's account have pointed out the
weaknesses in his explanation of how we gain such a concept by the
mental operation of abstraction on individual cases. For one thing, it
makes the incorrect assumption that various instances of a particular
concept share a common feature. Carruthers puts the objection as
follows:



> 
> In fact problems arise for empiricists even in connection with the
> very simplest concepts, such as those of colour. For it is false that
> all instances of a given colour share some common feature. In which
> case we cannot acquire the concept of that colour by abstracting the
> common feature of our experience. Thus consider the concept
> *red*. Do all shades of red have something in common? If so,
> what? It is surely false that individual shades of red consist, as it
> were, of two distinguishable elements a general redness together with
> a particular shade. Rather, redness consists in a continuous
> *range* of shades, each of which is only just distinguishable
> from its neighbors. Acquiring the concept *red* is a matter of
> learning the extent of the range. (1992, p. 59)
> 



For another thing, Locke's account of concept acquisition from
particular experiences seems circular: "For noticing or
attending to a common feature of various things presupposes that you
already possess the concept of the feature in question."
(Carruthers 1992, p. 55)



Consider in this regard Locke's account of how we gain our
concept of causation.



> 
> In the notice that our senses take of the constant vicissitude of
> things, we cannot but observe, that several particulars, both
> qualities and substances; begin to exist; and that they receive this
> their existence from the due application and operation of some other
> being. From this observation, we get our ideas of cause and effect.
> (*Essay*, 2.26.1)
> 



We get our concept of causation from our observation that some things
receive their existence from the application and operation of some
other things. Yet, to be able to make this observation, we must have
our minds primed to do so. Rationalists argue that we cannot make this
observation unless we already have the concept of causation.
Empiricists, on the other hand, argue that our minds are constituted
in a certain way, so that we can gain our ideas of causation and of
power in a non-circular manner.



Rationalists would argue that Locke's account of how we gain our
idea of power displays a similar circularity.



> 
> The mind being every day informed, by the senses, of the alteration of
> those simple ideas, it observes in things without; and taking notice
> how one comes to an end, and ceases to be, and another begins to exist
> which was not before; reflecting also on what passes within itself,
> and observing a constant change of its ideas, sometimes by the
> impression of outward objects on the senses, and sometimes by the
> determination of its own choice; and concluding from what it has so
> constantly observed to have been, that the like changes will for the
> future be made in the same things, by like agents, and by the like
> ways, considers in one thing the possibility of having any of its
> simple ideas changed, and in another the possibility of making that
> change; and so comes by that idea which we call power.
> (*Essay*, 2.21.1)
> 



We come by the idea of power though considering the possibility of
changes in our ideas made by experiences and our own choices. Yet, to
consider this possibility--of some things *making* a
change in others--we must already have a concept of power,
rationalists would say. Empiricists, on the other hand, would point
out, again, that what we actually need is for our minds to be able to
recognize this, by having the correct abilities and faculties. Just as
we don't need to have a concept telling us how it is that we
have binocular vision, being able to recognize change would be cashed
out by us having the requisite faculty enabling us to do so.



Another way to meet at least some of these challenges to an empiricist
account of the origin of our concepts is to revise our understanding
of the content of our concepts so as to bring them more in line with
what experience will clearly provide. Hume famously takes this
approach. Beginning in a way reminiscent of Locke, he distinguishes
between two forms of mental contents or "perceptions," as
he calls them: impressions and ideas. Impressions are the contents of
our current experiences: our sensations, feelings, emotions, desires,
and so on. Ideas are mental contents derived from impressions. Simple
ideas are copies of impressions; complex ideas are derived from
impressions by "compounding, transposing, augmenting or
diminishing" them. Given that all our ideas are thus gained from
experience, Hume offers us the following method for determining the
content of any idea and thereby the meaning of any term taken to
express it.



> 
> When we entertain, therefore, any suspicion that a philosophical term
> is employed without any meaning or idea (as is but too frequent), we
> need but inquire *from what impression is that supposed idea
> derived*? And if it be impossible to assign any, this will confirm
> our suspicion. (*Enquiry*, 2, p. 16)
> 



Using this test, Hume draws out one of the most important implications
of the empiricists' denial of the Innate Concept thesis. If
experience is indeed the source of all ideas, then our experiences
also determine the content of our ideas. Our ideas of causation, of
substance, of right and wrong have their content determined by the
experiences that provide them. Those experiences, Hume argues, are
unable to support the content that many rationalists and some
empiricists, such as Locke, attribute to the corresponding ideas. Our
inability to explain how some concepts, with the contents the
rationalists attribute to them, are gained from experience should not
lead us to adopt the Innate Concept thesis. It should lead us to
accept a more limited view of the contents for those concepts, and
thereby a more limited view of our ability to describe and understand
the world.



Consider, for example, our idea of causation. Descartes takes it to be
innate. Hume's empiricist account severely limits its content.
Our idea of causation is derived from a feeling of expectation rooted
in our experiences of the constant conjunction of similar causes and
effects.



> 
> It appears, then, that this idea of a necessary connection among
> events arises from a number of similar instances which occur, of the
> constant conjunction of these events; nor can that idea ever be
> suggested by any one of these instances surveyed in all possible
> lights and positions. But there is nothing in a number of instances,
> different from every single instance, which is supposed to be exactly
> similar, except only that after a repetition of similar instances the
> mind is carried by habit, upon the appearance of one event, to expect
> its usual attendant and to believe that it will exist. This
> connection, therefore, which we *feel* in the mind, this
> customary transition of the imagination from one object to its usual
> attendant, is the sentiment or impression from which we form the idea
> of power or necessary connection. (*Enquiry*, 7.2, p. 59)
> 



The source of our idea in experience determines its content.



> 
> Suitably to this experience, therefore, we may define a cause to be an
> object followed by another, and where all the objects, similar to the
> first are followed by objects similar to the second... We may,
> therefore, suitably to this experience, form another definition of
> cause and call it *an object followed by another, and whose
> appearance always conveys the thought of the other*.
> (*Enquiry*, 7.2, p. 60)
> 



Our claims, and any knowledge we may have, about causal connections in
the world turn out, given the limited content of our empirically based
concept of causation, to be claims and knowledge about the constant
conjunction of events and our own feelings of expectation. Thus, the
initial disagreement between rationalists and empiricists about the
source of our ideas leads to one about their content and thereby the
content of our descriptions and knowledge of the world.



Like philosophical debates generally, the rationalist/empiricist
debate ultimately concerns our position in the world, in this case our
position as rational inquirers. To what extent do our faculties of
reason and experience support our attempts to know and understand our
situation?