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ambiguity and is as simple as possible and in that system of expression to state fully all the different stages of the demonstration to be explained and to show that the passage from each one to the next takes place according to a rule which can evidently never authorize a passage from the representation of one state of things to a representation of a different state of things.

The first thing to be done, therefore, is to agree upon such an unambiguous and simple system of expression.
The present lecture will be devoted to a description in outline of such a system.
The present course is too short to enable me to do much toward illustrating the use of it.
But if you will only learn this system, which is very easy, and will then train yourselves in expressing facts in this way and reasoning in this