Elements of the philosophy of the human mind. By Dugald Stewart. Rev. and abridged, with critical and explanatory notes, for the use of colleges and schools. By Francis Bowen ...

390 RiEASON.
catoptrics and in dioptrics. In a sense perfectly analogous to
this, the definitions of geometry (all of which are merely hypothetical) are the first principles of reasoning in the subsequent demonstrations, and the basis on which the whole fabric
of the science rests.
I have called this the proper acceptation of the word, bet
cause it is that in which it is most fiequently used by the best
writers. It is also most agreeable to the literal meaning which
its etymology suggests, expressing the original point froml which
our reasoning sets out or commences.
Dr. Reid often uses the word in this sense, as, for example,
in the following sentence: " From three or four axioms, which
he calls reygule philosophandi, together with the phenomena
observed by the senses, which he likewise lays down as first
principles, Newton deduces, by strict reasoning, the propositions contained in the third book of his Principia, and in his
Optics."
Alnother significction of'first principles.' - On other occasions, he uses the same word to denote those elemental tr'utths (if
I may use the expression) which are virtually taken for granted
or assumed, in every step of our reasoning; and without which,
although no consequences can be directly inferred fiom them, a
train of reasoning would be impossible. Of this kind, in nmathematics, are the axioms, or (as Mr. Locke and others frequently
call them) the maxims; in physics, a belief of the continuance
of the Laws of ~atture; in all our reasonings, without exception, a belief in our own identity, and in the evidence of imeemory. Such truths are the last elements into which reasoning
resolves itself, when subjected to a metaphysical analysis, and
which no person but a metaphysician or a logician ever thinlks
of stating in the form of propositions, or even of expressing_
verbally to himself. It is to truths of this description, that
Locke seems, in general, to apply the name of maxims; and,
in this sense, it is unquestionably true, that no science (not even
geometry) is founded on maxims as its first principles.
Distinction between principles of reasoning and elements of
reasoning. - In one sense of the word principle, indeed, max