## 1. Life and Works



Leucippus is variously said to have been born in Elea, Abdera or
Miletus (DK 67A1). His dates are unknown, other than that he lived
during the fifth century BCE. Diogenes Laertius reports that he was a
student of Parmenides' follower Zeno (DK 67A1). Zeno is best
known for paradoxes suggesting that motion would be impossible if a
magnitude could be divided into an infinite number of parts, each of
which must be traversed, and other absurdities associated with taking
magnitudes to be infinitely divisible. The likelihood that atomism
is thought to have been formulated at least partly in response to
these arguments may account for the story that Leucippus was a student
of Zeno.



The extent of Leucippus' contribution to the developed atomist
theory is unknown. His relationship to Democritus, and even his very
existence, was a subject of considerable controversy in nineteenth
century scholarship (Graham 2008). Most reports on early Greek atomism
refer to the views of Democritus alone, or to both atomists together;
Epicurus seems even to have denied that there was a philosopher
Leucippus (DK 67A2). Aristotle certainly ascribes the foundation of
the atomist system to Leucippus. Leucippus is sometimes said to have
been the author of a work called the *Great World-System*; one
surviving quotation is said to have come from a work *On
Mind*.


## 2. Atomist Doctrine



Leucippus is named by most sources as the originator of the theory
that the universe consists of two different elements, which he called
'the full' or 'solid,' and 'the
empty' or 'void'. Both the void and the solid atoms
within it are thought to be infinite, and between them to constitute
the elements of everything. Because little is known of
Leucippus' views and his specific contributions to atomist
theory, a fuller discussion of the developed atomist doctrine is found
in the entry for Democritus.



Early Greek atomism is generally taken to have been formulated in
response to the Eleatic claim that 'what is' must be one
and unchanging, because any assertion of differentiation or change
within 'what is' involves the assertion of 'what is
not,' an unintelligible concept. While Parmenides'
argument is difficult to interpret, he was understood in antiquity to
have forced philosophers after him to explain how change is possible
without supposing that something comes from 'what is not,'
i.e. nothing. Aristotle tells us that Leucippus tried to formulate a
theory that is consistent with the evidence of the senses that change
and motion and a multiplicity of things exists in the world (DK 67A7).
In the atomist system, many of the changes we perceive are merely
apparent: the real constituents of being persist unchanged, merely
rearranging themselves into new combinations that form the world of
appearance. Like Parmenidean Being, the atoms cannot change or
disintegrate into 'what is not' and each is a solid unit;
nonetheless, the combinations of atoms that form the world of
appearance continually alter. Aristotle cites an analogy to the
letters of the alphabet, which can produce a multitude of different
words from a few elements in combinations; the differences all stem
from the shape (*schema*) of the letters, as A differs
from N; by their arrangement (*taxis*), as AN differs from NA;
and by their positional orientation (*thesis*), as N differs
from Z (DK 67A6).



Leucippus also reportedly accepted the Eleatic Melissus'
argument that void is necessary for motion, but took this to be
evidence that, since we experience motion, there must be void (DK
67A7). The reason for positing smallest indivisible magnitudes is also
reported to be a response to Zeno's paradoxes that arise from
assuming magnitudes are infinitely divisible (DK 29A22). Leucippus is
reported to hold that the atoms are always in motion (DK 67A18).
Aristotle criticizes him for not offering an account that says not
only why a particular atom is moving (because it collided with
another) but why there is motion at all. Because the atoms are
indestructible and unchangeable, their properties presumably stay the
same through all time.



As Diogenes Laertius reports Leucippus' cosmology, worlds or
*kosmoi* are formed when groups of atoms combine to form a
cosmic whirl, which causes the atoms to separate out and sort by like
kind. A sort of membrane of atoms forms out of the circling atoms,
enclosing others within it, and creating pressure by whirling. The
outer membrane continually acquires other atoms from outside when it
contacts them, which get ignited as they revolve and form the stars,
with the sun in the outermost circle. Worlds are formed, grow and
perish, according to a kind of necessity (DK 67A1).



One direct quotation preserved from Leucippus says that nothing
happens in vain (*maten*) but everything from
*logos* and by necessity (DK 67B2). This has been found
puzzling, since the reference to *logos* might seem to suggest
that things are ruled by reason, an idea that Democritus' system
excludes. Either Leucippus' system is different in this respect
from that of Democritus, or the reference to *logos* here
cannot be to a controlling mind. Barnes takes there to be no grounds
for preferring either interpretation (Barnes 1984), but Taylor argues
that Leucippus' position is that an account (or *logos*)
can be given of the causes of all occurrences (Taylor 1999, p. 189).
There is nothing in other reports to suggest that Leucippus endorsed
the idea of a universal intelligence governing events.



Aristotle frequently pairs Leucippus and Democritus in his reports,
including his account of the motivation for positing atoms and void.
In particular, Aristotle associates Leucippus as well as Democritus
with the deliberately paradoxical assertion that 'being is no
more than not-being,' i.e., that void exists as much as the full
or solid (DK 67A6). Schofield (2002) has argued that the more careful
account in Simplicius shows that the *ou mallon* or 'no
more' doctrine is due to Democritus. Following this lead, Graham
(2008) suggests a new reading of Leucippus, wherein the distinction
between atom and void is actually based on a reading of
Parmenides' Doxa, his cosmological account. Rather than logical
abstractions, Being and Not-being, Leucippus' atoms would in
essence be based on Parmenides' cosmological contraries, night
and light. If this line of interpretation is followed,
Leucippus' notion of atom and void might have been rather
different from Democritus', and Aristotle's tendency to
refer to the two in conjunction somewhat misleading.