Deductive Logic | Page 3

particle of matter
in the universe.
§ 9. The word 'law' is transferred by a metaphor from one of these
senses to the other. The effect of such a command as that described
above is to produce a certain amount of uniformity in the conduct of
men, and so, where we observe uniformity in nature, we assume that it
is the result of such a command, whereas the only thing really known to
us is the fact of uniformity itself.
§ 10. Now in which of these two senses are we using the term 'laws of
thought'? The laws of the land, it is plain, are often violated, whereas

the laws of nature never can be so [Footnote: There is a sense in which
people frequently speak of the laws of nature being violated, as when
one says that intemperance or celibacy is a violation of the laws of
nature, but here by 'nature' is meant an ideal perfection in the
conditions of existence.]. Can the laws of thought be violated in like
manner with the laws of the land? Or are they inviolable like the laws
of nature?
§ 11. In appearance they can be, and manifestly often are violated-for
how else could error be possible? But in reality they can not. No man
ever accepts a contradiction when it presents itself to the mind as such:
but when reasoning is at all complicated what does really involve a
contradiction is not seen to do so; and this sort of error is further
assisted by the infinite perplexities of language.
§ 12. The laws of thought then in their ultimate expression are certain
uniformities which invariably hold among mental phenomena, and so
far they resemble the laws of nature: but in their complex applications
they may be violated owing to error, as the laws of the land may be
violated by crime.
§ 13. We have now to determine the meaning of the expression 'formal
laws of thought.'
§ 14. The distinction between form and matter is one which pervades
all nature. We are familiar with it in the case of concrete things. A cup,
for instance, with precisely the same form, may be composed of very
different matter-gold, silver, pewter, horn or what not?
§ 15. Similarly in every act of thought we may distinguish two things--
(1) the object thought about,
(2) the way in which the mind thinks of it.
The first is called the Matter; the second the Form of Thought.
§ 16. Now Formal, which is another name for Deductive Logic, is

concerned only with the way in which the mind thinks, and has nothing
to do with the particular objects thought about.
§ 17. Since the form may be the same, whilst the matter is different, we
may say that formal logic is concerned with the essential and necessary
elements of thought as opposed to such as are accidental and contingent.
By 'contingent' is meant what holds true in some cases, but not in
others. For instance, in the particular case of equilateral triangles it is
true to say, not only that 'all equilateral triangles are equiangular,' but
also that 'all equiangular triangles are equilateral.' But the evidence for
these two propositions is independent. The one is not a formal
consequence of the other. If it were, we should be able to apply the
same inference to all matter, and assert generally that if all A is B, all B
is A, which it is notorious that we cannot do.
§ 18. It remains now for the full elucidation of our definition to
determine what is meant by 'science.'
§ 19. The question has often been discussed whether logic is a science
or an art. The answer to it must depend upon the meaning we assign to
these terms.
§ 20. Broadly speaking, there is the same difference between Science
and Art as there is between knowing and doing.
Science is systematized knowledge; Art is systematized action. Science
is acquired by study; Art is acquired by practice.
§ 21. Now logic is manifestly a branch of knowledge, and does not
necessarily confer any practical skill. It is only the right use of its rules
in thinking which can make men think better. It is therefore, in the
broad sense of the terms, wholly a science and not at all an art.
§ 22. But this word 'art,' like most others, is ambiguous, and is often
used, not for skill displayed in practice, but for the knowledge
necessary thereto. This meaning is better conveyed by the term
'practical science.'

§ 23. Science is either speculative or practical. In the first case we study
merely that we may know; in the latter that we may do.
Anatomy is a speculative science; Surgery is a practical science.
In the