e observed in Lucretius'
praises of him above, even physics had but one purpose or interest, to
free the soul from [370] terrors of the unseen. Thus philosophy was
mainly concerned with conduct, _i.e._ with Ethics, but secondarily and
negatively with Physics, to which was appended what Epicurus called
Canonics, or the science of testing, that is, a kind of logic.

[371]

Beginning with _Canonics_, as the first part of philosophy in order of
time, from the point of view of human knowledge, Epicurus laid it down
that the only source of knowledge was the senses, which gave us an
immediate and true perception of that which actually came into contact
with them. Even the visions of madmen or of dreamers he considered
were in themselves true, being produced by a physical cause of some
kind, of which these visions were the direct and immediate report.
Falsity came in with {215} people's interpretations or imaginations
with respect to these sensations.

Sensations leave a trace in the memory, and out of similarities or
analogies among sensations there are developed in the mind general
notions or types, such as 'man,' 'house,' which are also true, because
[373] they are reproductions of sensations. Thirdly, when a sensation
occurs, it is brought into relation in the mind with one or more of
these types or notions; this is _predication_, true also in so far as
its elements are true, but capable of falsehood, as subsequent or
independent sensation may prove. If supported or not contradicted by
sensation, it is or may be true; if contradicted or not supported by
sensation, it is or may be false. The importance of this statement of
the canon of truth or falsehood will be understood when we come to the
physics of Epicurus, at the basis of which is his theory of Atoms,
which by their very nature can never be directly testified to by
sensation.

[374]

This and no more was what Epicurus had to teach on the subject of
logic. He had no theory of definition, or division, or ratiocination,
or refutation, or explication; on all these matters Epicurus was, as
Cicero said, 'naked and unarmed.' Like most self-taught or ill-taught
teachers, Epicurus trusted to his dogmas; he knew nothing and cared
nothing for logical defence.

{216}

[375]

In his _Physics_ Epicurus did little more than reproduce the doctrine
of Democritus. He starts from the fundamental proposition that
'nothing can be produced from nothing, nothing can real