Sec. 3.  Universal Propositions, of course, cannot always be proved by syllogisms; because to prove a universal proposition by a syllogism, its premises must be universal propositions; and, then, these must be proved by others.  This process may sometimes go a little way, thus:  All men are mortal, because All animals are; and All animals are mortal, because All composite bodies are subject to dissolution. Were there no limit to such sorites, proof would always involve a regressus ad infinitum, for which life is too short; but, in fact, prosyllogisms soon fail us.

Clearly, the form of the Syllogism must itself be misleading if the universal proposition is so:  if we think that premises prove the conclusion because they themselves have been established by detailed observation, we are mistaken.  The consideration of any example will show this.  Suppose any one to argue: 

      All ruminants are herbivorous;
      Camels are ruminants: 
    .’.  Camels are herbivorous.

Have we, then, examined all ruminants?  If so, we must have examined all camels, and cannot need a syllogism to prove their herbivorous nature:  instead of the major premise proving the conclusion, the proof of the conclusion must then be part of the proof of the major premise.  But if we have not examined all ruminants, having omitted most giraffes, most deer, most oxen, etc., how do we know that the unexamined (say, some camels) are not exceptional?  Camels are vicious enough to be carnivorous; and indeed it is said that Bactrian camels will eat flesh rather than starve, though of course their habit is herbivorous.

Or, again, it is sometimes urged that—­

      All empires decay: 
    .’.  Britain will decay.

This is manifestly a prediction:  at present Britain flourishes, and shows no signs of decay.  Yet a knowledge of its decay seems necessary, to justify any one in asserting the given premise.  If it is a question whether Britain will decay, to attempt (while several empires still flourish) to settle the matter by asserting that all empires decay, seems to be ‘a begging of the question.’  But although this latter case is a manifest prediction, it does not really differ from the former one; for the proof that camels are herbivorous has no limits in time.  If valid, it shows not only that they are, but also that they will be, herbivorous.

Hence, to resort to a dilemma, it may be urged:  If all the facts of the major premise of any syllogism have been examined, the syllogism is needless; and if some of them have not been examined, it is a petitio principii.  But either all have been examined, or some have not.  Therefore; the syllogism is either useless or fallacious.