C. S. Peirce Manuscripts

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with the country, no man of it would ever be of the slightest use to you in laying out your detailed plans? To that he must have rejoined, "I do not say that because I might wish to stick in pins in order to trace out and study the daily changes of the situations." To that, again, my surrejoinder should have been, "Well, General, that precisely corresponds to the advantage of a diagram of the course of thought. Indeed, just there is the advantage of diagrams in general. Namely, one can make exact experiments upon diagrams, and look out for unintended change thereby brought about in the relations of different parts of the diagram to one another. These operations in reasoning take the place of the experiments upon real things that one performs in chemical and physical research. Chemists have sometimes described

πλ 3 experimentation as putting questions to "nature," experiments upon diagrams are questions not to the nature of the relations concerned." Maybe, the general would suggest that there is a good deal of difference between experiments like the chemists, which are trials made upon the very substance whose behavior is in question, and experiments made upon diagrams, which has no real connexion with the things the diagrams represent. The proper response to that and the only proper one making a point that a novice in logic would be pretty sure to miss, would be "You are entirely right in saying that the chemist experiments upon the very object under investigation, although, after the experiment is done, the particular sample operated upon may be thrown away, as having no further