. They are what we have called reasons. If we are to
explain the existence of an object in the universe it may be necessary
to introduce formal causes, concepts, to show why the thing exists, to
show in fact its reasons. But science makes no attempt to explain the
existence of objects. It takes their {271} existence for granted, and
seeks to trace their history and their relations to each other.
Therefore it does not require formal causes. It seeks to work out the
mechanical view of the universe, and therefore considers only
mechanical causes. But Aristotle's theory, as being philosophy rather
than science, includes both the principles of mechanism and teleology.

It was not Aristotle's habit to propound his theories as if they were
something absolutely new, sprung for the first time out of his own
brain. In attacking any problem, his custom was to begin by
enumerating current and past opinions, to criticise them, to reject
what was valueless in them, to retain the residue of truth, and to add
to it his own suggestions and original ideas. The resultant of this
process was his own theory, which he thus represented, not as
absolutely new, but as a development of the views of his predecessors.
This course he follows also in the present instance. The first book of
the "Metaphysics" is a history of all previous philosophy, from Thales
to Plato, undertaken with the object of investigating how far the four
causes had been recognized by his predecessors. The material cause, he
says, had been recognized from the first. The Ionics believed in this
and no other cause. They sought to explain everything by matter,
though they differed among themselves as to the nature of the material
cause, Thales describing it as water, Anaximenes as air. Later
philosophers also gave different accounts of it, Heracleitus thinking
it was fire, Empedocles the four elements, Anaxagoras an indefinite
number of kinds of matter. But the point is that they all recognized
the necessity for a material cause of some sort to explain the
universe.

{272}

The earliest thinkers, then, the Ionics, assumed only this one cause.
But as thought advanced, says Aristotle, and other philosophers came
upon the scene, "the thing itself guided them." It was seen that a
second cause was necessary to explain the motion and becoming of
things. For matter itself does not produce its motion. Wood is not the
cause of its becoming a bed, nor is brass the cause of its becomi