Now that we have established these distinctions, we must proceed
to consider causes, their character and number. Knowledge is the
object of our inquiry, and men do not think they know a thing till
they have grasped the "why" of (which is to grasp its primary
cause). So clearly we too must do this as regards both coming to be
and passing away and every kind of physical change, in order that,
knowing their principles, we may try to refer to these principles each
of our problems.

    In one sense, then, (1) that out of which a thing comes to be and
which persists, is called "cause", e.g. the bronze of the statue,
the silver of the bowl, and the genera of which the bronze and the
silver are species.

    In another sense (2) the form or the archetype, i.e. the statement
of the essence, and its genera, are called "causes" (e.g. of the
octave the relation of 2:1, and generally number), and the parts in
the definition.

    Again (3) the primary source of the change or coming to rest; e.g.
the man who gave advice is a cause, the father is cause of the
child, and generally what makes of what is made and what causes change
of what is changed.

    Again (4) in the sense of end or "that for the sake of which" a
thing is done, e.g. health is the cause of walking about. ("Why is
he walking about?" we say. "To be healthy", and, having said that,
we think we have assigned the cause.) The same is true also of all the
intermediate steps which are brought about through the action of
something else as means towards the end, e.g. reduction of flesh,
purging, drugs, or surgical instruments are means towards health.
All these things are "for the sake of" the end, though they differ
from one another in that some are activities, others instruments.

    This then perhaps exhausts the number of ways in which the term
"cause" is used.

    As the word has several senses, it follows that there are several
causes of the same thing not merely in virtue of a concomitant
attribute), e.g. both the art of the sculptor and the bronze are
causes of the statue. These are causes of the statue qua statue, not
in virtue of anything else that it may be-only not in the same way,
the one being the material cause, the other the cause whence the
motion comes. Some things cause each other reciprocally, e.g. hard
work causes fitness and vice versa, but again not in the same way, but
the one as end, the other as the origin of change. Further the same
thing is the cause of contrary results. For that which by its presence
brings about one result is sometimes blamed for bringing about the
contrary by its absence. Thus we ascribe the wreck of a ship to the
absence of the pilot whose presence was the cause of its safety.

    All the causes now mentioned fall into four familiar divisions.
The letters are the causes of syllables, the material of artificial
products, fire, &c., of bodies, the parts of the whole, and the
premisses of the conclusion, in the sense of "that from which". Of
these pairs the one set are causes in the sense of substratum, e.g.
the parts, the other set in the sense of essence-the whole and the
combination and the form. But the seed and the doctor and the adviser,
and generally the maker, are all sources whence the change or
stationariness originates, while the others are causes in the sense of
the end or the good of the rest; for "that for the sake of which"
means what is best and the end of the things that lead up to it.
(Whether we say the "good itself or the "apparent good" makes no
difference.)

    Such then is the number and nature of the kinds of cause.

    Now the modes of causation are many, though when brought under heads
they too can be reduced in number. For "cause" is used in many
senses and even within the same kind one may be prior to another (e.g.
the doctor and the expert are causes of health, the relation 2:1 and
number of the octave), and always what is inclusive to what is
particular. Another mode of causation is the incidental and its
genera, e.g. in one way "Polyclitus", in another "sculptor" is the
cause of a statue, because "being Polyclitus" and "sculptor" are
incidentally conjoined. Also the classes in which the incidental
attribute is included; thus "a man" could be said to be the cause of a
statue or, generally, "a living creature". An incidental attribute too
may be more or less remote, e.g. suppose that "a pale man" or "a
musical man" were said to be the cause of the statue.

    All causes, both proper and incidental, may be spoken of either as
potential or as actual; e.g. the cause of a house being built is
either "house-builder" or "house-builder building".

    Similar distinctions can be made in the things of which the causes
are causes, e.g. of "this statue" or of "statue" or of "image"
generally, of "this bronze" or of "bronze" or of "material" generally.
So too with the incidental attributes. Again we may use a complex
expression for either and say, e.g. neither "Polyclitus" nor
"sculptor" but "Polyclitus, sculptor".

    All these various uses, however, come to six in number, under each
of which again the usage is twofold. Cause means either what is
particular or a genus, or an incidental attribute or a genus of
that, and these either as a complex or each by itself; and all six
either as actual or as potential. The difference is this much, that
causes which are actually at work and particular exist and cease to
exist simultaneously with their effect, e.g. this healing person
with this being-healed person and that house-building man with that
being-built house; but this is not always true of potential
causes--the house and the housebuilder do not pass away
simultaneously.

    In investigating the cause of each thing it is always necessary to
seek what is most precise (as also in other things): thus man builds
because he is a builder, and a builder builds in virtue of his art
of building. This last cause then is prior: and so generally.

    Further, generic effects should be assigned to generic causes,
particular effects to particular causes, e.g. statue to sculptor, this
statue to this sculptor; and powers are relative to possible
effects, actually operating causes to things which are actually
being effected.

    This must suffice for our account of the number of causes and the
modes of causation.