500 
PROFESSOR JEVONS ON THE MECHANICAL 
them by a subsequent process of interpretation. It is surely sufficient to condemn the 
peculiar mathematical form of Boole’s method, that if it were the true form of logical 
deduction, only well-trained mathematicians could ever comprehend the action of those 
laws of thought, on the habitual use of which our existence as superior beings depends. 
11. Having made Boole’s logical works a subject of study for many years past, I endea- 
voured to show in my work on Pure Logic* that the mysterious mathematical forms 
of Boole’s logic are altogether superfluous, and that in one point of great importance, 
the employment of exclusive instead of unexclusive alternatives, he was deeply mis- 
taken. Rejecting the mathematical dress and the erroneous conditions of his symbols, 
we arrive at a logical method of the utmost generality and simplicity. In a later workf 
I have given a more mature and clear view of the principles of this Calculus of Logic, 
and of the processes of reasoning in general, and to these works I must refer readers 
who may be interested in the speculative or theoretical views of the subject. In the 
present paper my sole purpose is to bring forward a visible and tangible proof that a 
new system of logical deduction has been attained. The logical machine which I am 
about to describe is no mere model illustrative of the fixed forms of the syllogism. It 
is an analytical engine of a very simple character, which performs a complete analysis of 
any logical problem impressed upon it. By merely reading down the premises or data 
of an argument on a key board representing the terms, conjunctions, copula, and stops 
of a sentence, the machine is caused to make such a comparison of those premises that it 
becomes capable of returning any answer which may be logically deduced from them. It 
It is charged, as it were, with a certain amount of information which can be drawn from 
it again in any logical form which may be desired. The actual process of logical deduc- 
tion is thus reduced to a purely mechanical form, and we arrive at a machine embodying 
the 4 Laws of Thought,’ which may almost be said to fulfil in a substantial manner the 
vague idea of an organon or instrumental logic which has flitted during many cen- 
turies before the minds of logicians. 
12. As the ordinary views of logic and the doctrine of the syllogism would give little 
or no assistance in comprehending the action of the machine, I find it necessary to pre- 
face the description of the machine itself with a brief and simple explanation of the 
principles of the indirect method of inference which is embodied in it, avoiding any 
reference to points of abstract or speculative interest which could not be suitably treated 
in the present paper. 
13. Whatever be the form in which the rules of deductive logic are presented, their 
validity must rest ultimately upon the Three Fundamental Laws of Thought which de- 
velope the nature of Identity and Diversity. These laws are three in number. The 
first appears to give a definition of Identity by asserting that a thing is identical with 
* Pure Logic, or the Logic of Quality apart from Quantity : with Remarks on Boole’s System, and on the 
relation of Logic and Mathematics. London, 1864 (Stanford,). 
f The Substitution of Similars, the True Principle of Reasoning : derived from a Modification of Akistotle’s 
Dictum. London, 1869 (Macmillan). 
