ABSTRACT
Formal immediate inference is trivial. When we seem to have inferred a non-trivial conclusion from a single premiss it is because we have tacitly made assumptions or have pre supposed a premiss without noticing that we have done so. At least two premisses are required for a properly formal inference which is not trivial. Such inference is mediate in ference. It is seldom that we state both premisses explicitly, but it is possible to find examples. Sir Henry CampbellBannerman was making an informal speech to his neighbours at Montrose. In the course of it he said: ‘An old friend of mine, Wilfrid Lawson, was accustomed to say: “ The man who walks on a straight road never loses his way.5’ Well, I flatter myself that I have walked on a pretty straight road, probably because it was easier, and accordingly I have not gone astray.5* The conclusion I have not gone astray is implied by the conjoint assertion of two premisses, The man who walks on a straight road never loses his way (i.e. does not go astray) and I have walked on a (pretty) straight road. No one should have any difficulty in seeing that the conclusion does indeed follow from the premisses. Arguments of this kind, in which a conclusion is inferred from two premisses, can often be stated in a traditional form called the syllogism. For example:
(i) All human beings are liable to make mistakes. All philosophers are human beings. .*. All philosophers are liable to make mistakes.
