The observation requisite for the selection of
premisses may sometimes involve little more than the
reflective contemplation of certain of the most familiar
of every-day facts. But it is to be remembered that
the economist does not always work from one and the
same set of assumptions ; and in some cases knowledge
of a much more extended character is required in order



230 THE DEDUCTIVE METHOD. [CHAPj

to determine what the premisses shall be. This remark
applies to the working out of the theory of the foreign
exchanges, of movements in general prices, of the effects
of trade-unions or of machinery on wages, and the like.
