origin of memory; that man alone possesses recollection, but
animals share with him memory--memory being unintentional or
spontaneous, but recollection implying voluntary exertion or a search;
that recollection is necessary for acting with design. It is doubtful
whether Aristotle believed in the immortality of the soul, no decisive
passage to that effect occurring in such of his works as are extant.

[Sidenote: Causes of Aristotle's success and failure.]

Aristotle, with a correct and scientific method, tried to build up a
vast system when he was not in possession of the necessary data. Though
a very learned man, he had not sufficient knowledge; indeed, there was
not sufficient knowledge at that time in the world. For many of the
assertions I have quoted in the preceding paragraph there was no kind of
proof; many of them also, such as the settling of the heavy and the rise
of the light, imply very poor cosmic ideas. It is not until he deals
with those branches, such as comparative anatomy and natural history, of
which he had a personal and practical knowledge, that he begins to write
well. Of his physiological conclusions, some are singularly felicitous;
his views of the connected chain of organic forms, from the lowest to
the highest, are very grand. His metaphysical and physical
speculations--for in reality they are nothing but speculations--are of
no kind of value. His successful achievements, and also his failures,
conspicuously prove the excellence of his system. He expounded the true
principles of science, but failed to apply them merely for want of
materials. His ambition could not brook restraint. He would rather
attempt to construct the universe without the necessary means than not
construct it at all.

Aristotle failed when he abandoned his own principles, and the magnitude
of his failure proves how just his principles were; he succeeded when he
adhered to them. If anything were wanting to vindicate their correctness
and illustrate them, it is supplied by the glorious achievements of the
Alexandrian school, which acted in physical science as Aristotle had
acted in natural history, laying a basis solidly in observation and
experiment, and accomplishing a like durable and brilliant result.

[Sidenote: Biography of Zeno.]

From Aristotle it is necessary to turn to Zeno, for the Peripatetics and
Stoics stand in parallel lines. The social conditions existing in Greece
at the time of Epicurus may in some degree