Posterior Analytics   

(2) The universal has not a separate being over against groups of
singulars. Demonstration nevertheless creates the opinion that its
function is conditioned by something like this-some separate entity
belonging to the real world; that, for instance, of triangle or of
figure or number, over against particular triangles, figures, and
numbers. But demonstration which touches the real and will not mislead
is superior to that which moves among unrealities and is delusory. Now
commensurately universal demonstration is of the latter kind: if we
engage in it we find ourselves reasoning after a fashion well
illustrated by the argument that the proportionate is what answers
to the definition of some entity which is neither line, number, solid,
nor plane, but a proportionate apart from all these. Since, then, such
a proof is characteristically commensurate and universal, and less
touches reality than does particular demonstration, and creates a
false opinion, it will follow that commensurate and universal is
inferior to particular demonstration.
We may retort thus. (1) The first argument applies no more to
commensurate and universal than to particular demonstration. If
equality to two right angles is attributable to its subject not qua
isosceles but qua triangle, he who knows that isosceles possesses that
attribute knows the subject as qua itself possessing the attribute, to
a less degree than he who knows that triangle has that attribute. To
sum up the whole matter: if a subject is proved to possess qua
triangle an attribute which it does not in fact possess qua
triangle, that is not demonstration: but if it does possess it qua
triangle the rule applies that the greater knowledge is his who
knows the subject as possessing its attribute qua that in virtue of
which it actually does possess it. Since, then, triangle is the
wider term, and there is one identical definition of triangle-i.e. the
term is not equivocal-and since equality to two right angles belongs
to all triangles, it is isosceles qua triangle and not triangle qua
isosceles which has its angles so related. It follows that he who
knows a connexion universally has greater knowledge of it as it in
fact is than he who knows the particular; and the inference is that
commensurate and universal is superior to particular demonstration.
(2) If there is a single identical definition i.e. if the
commensurate universal is unequivocal-then the universal will
possess being not less but more than some of the particulars, inasmuch
as it is universals which comprise the imperishable, particulars
that tend to perish.
(3) Because the universal has a single meaning, we are not therefore
compelled to suppose that in these examples it has being as a
substance apart from its particulars-any more than we need make a
similar supposition in the other cases of unequivocal universal
predication, viz. where the predicate signifies not substance but
quality, essential relatedness, or action. If such a supposition is
entertained, the blame rests not with the demonstration but with the
hearer.
(4) Demonstration is syllogism that proves the cause, i.e. the
reasoned fact, and it is rather the commensurate universal than the
particular which is causative (as may be shown thus: that which
possesses an attribute through its own essential nature is itself
the cause of the inherence, and the commensurate universal is primary;
hence the commensurate universal is the cause). Consequently
commensurately universal demonstration is superior as more
especially proving the cause, that is the reasoned fact.
(5) Our search for the reason ceases, and we think that we know,
when the coming to be or existence of the fact before us is not due to
the coming to be or existence of some other fact, for the last step of
a search thus conducted is eo ipso the end and limit of the problem.
Thus: 'Why did he come?' 'To get the money-wherewith to pay a
debt-that he might thereby do what was right.' When in this regress we
can no longer find an efficient or final cause, we regard the last
step of it as the end of the coming-or being or coming to be-and we