It has been recently pointed out to me, however, that the Rev. Robert Harley did draw attention, at the Nottingham Meeting of the British Association, in 1866, to Leibnitz’ anticipations of Boole’s laws of logical notation,8 and I am informed that Boole, about a year after the publication of his Laws of Thought, was made acquainted with these anticipations by R. Leslie Ellis.
There seems to have been at least one other German logician who discovered, or adopted, the principle of substitution. Reusch, in his Systema Logicum, published in 1734, laboured to give a broader basis to the Dictum de Omni et Nullo. He argues, that “the whole business of ordinary reasoning is accomplished by the substitution of ideas in place of the subject or predicate of the fundamental proposition. This some call the equation of thoughts.” But, in the hands of Reusch, substitution does not seem to lead to simplicity, since it has to be carried on according to the rules of Equipollence, Reciprocation, Subordination, and Co-ordination.9 Reusch is elsewhere spoken of10 as the “celebrated Reusch”; nevertheless, I have not been able to find a copy of his book in London, even in the British Museum Library; it is not mentioned in the printed catalogue of the Bodleian Library; Messrs. Asher have failed to obtain it for me by advertisement in Germany; and Professor Adamson has been equally unsuccessful. From the way in which the principle of substitution is mentioned by Reusch, it would seem likely that other logicians of the early part of the eighteenth century were acquainted with it; but, if so, it is still more curious that recent historians of logical science have overlooked the doctrine.
It is a strange and discouraging fact, that true views of logic should have been discovered and discussed from one to two centuries ago, and yet should have remained, like George Bentham’s work in this century, without influence on the subsequent progress of the science. It may be regarded as