If, indeed, we definitely limit the time, or place, or quantity of matter to be explored, we may sometimes learn, within the given limits, all that there is to know:  as all the bones of a particular animal, or the list of English monarchs hitherto, or the names of all the members of the House of Commons at the present time.  Such cases, however, do not invalidate the above logical truth that few general terms are exhaustively known in their denotation; for the very fact of assigning limits of time and place impairs the generality of a term.  The bones of a certain animal may be all examined, but not the bones of all animals, nor even of one species.  The English monarchs that have reigned hitherto may be known, but there may be many still to reign.

The general terms, then, with which Logic is chiefly concerned, the names of Causes and Kinds, such as gravitation, diseases, social events, minerals, plants and animals, stand for some facts that are, or have been, known, and for a great many other similar ones that have not been, and never will be, known.  The use of a general term depends not upon our direct knowledge of everything comprised in its denotation, but upon our readiness to apply it to anything that has its connotation, whether we have seen the thing or not, and even though we never can perceive it; as when a man talks freely of the ichthyosaurus, or of the central heat of planets, or of atoms and ether.

Hence Universal Propositions, which consist of general terms, deceive us, if we suppose that their predicates are directly known to be related to all the facts denoted by their subjects.  In exceptional cases, in which the denotation of a subject is intentionally limited, such exhaustive direct knowledge may be possible; as that “all the bones of a certain animal consist of phosphate of lime,” or that every member of the present Parliament wears a silk hat.  But what predication is possible concerning the hats of all members of Parliament from the beginning?  Ordinarily, then, whilst the relation of predicate to subject has been observed in some cases, in much the greater number of cases our belief about it depends upon something besides observation, or may be said (in a certain sense) to be taken on trust.

‘All rabbits are herbivorous’:  why do we believe that?  We may have seen a few wild rabbits feeding:  or have kept tame ones, and tried experiments with their diet; or have read of their habits in a book of Natural History; or have studied the anatomy and physiology of the digestive system in many sorts of animals:  but with whatever care we add testimony and scientific method to our own observation, it still remains true that the rabbits observed by ourselves and others are few in comparison with those that live, have lived and will live.  Similarly of any other universal proposition; that it ‘goes beyond the evidence’ of direct observation plainly follows from the fact that the general terms, of which such propositions consist, are never exhaustively known in their denotation.  What right have we then to state Universal Propositions?  That is the problem of Inductive Logic.