Sec. 4.  A way of escape from this dilemma is provided by distinguishing between the formal and material aspects of the syllogism considered as a means of proof.  It begs the question formally, but not materially; that is to say, if it be a question whether camels are herbivorous, and to decide it we are told that ‘all ruminants are,’ laying stress upon the ‘all,’ as if all had been examined, though in fact camels have not been, then the question as to camels is begged.  The form of a universal proposition is then offered as evidence, when in fact the evidence has not been universally ascertained.  But if in urging that ’all ruminants are herbivorous’ no more is meant than that so many other ruminants of different species are known to be herbivorous, and that the ruminant stomach is so well adapted to a coarse vegetable diet, that the same habit may be expected in other ruminants, such as camels, the argument then rests upon material evidence without unfairly implying the case in question.  Now the nature of the material evidence is plainly this, that the resemblance of camels to deer, oxen, etc., in chewing the cud, justifies us in believing that they have a further resemblance in feeding on herbs; in other words, we assume that resemblance is a ground of inference.

Another way of putting this difficulty which we have just been discussing, with regard to syllogistic evidence, is to urge that by the Laws of Syllogism a conclusion must never go beyond the premises, and that therefore no progress in knowledge can ever be established, except by direct observation.  Now, taking the syllogism formally, this is true:  if the conclusion go beyond the premises, there must be either four terms, or illicit process of the major or minor term.  But, taking it materially, the conclusion may cover facts which were not in view when the major premise was laid down; facts of which we predicate something not as the result of direct observation, but because they resemble in a certain way those facts which had been shown to carry the predicate when the major premise was formed.

‘What sort of resemblance is a sufficient ground of inference?’ is, therefore, the important question alike in material Deduction and in Induction; and in endeavouring to answer it we shall find that the surest ground of inference is resemblance of causation.  For example, it is due to causation that ruminants are herbivorous.  Their instincts make them crop the herb, and their stomachs enable them easily to digest it; and in these characters camels are like the other ruminants.

Sec. 5.  In ch. ix, Sec. 3, the Dictum de omni et nullo was stated:  ’Whatever may be predicated of a term distributed may be predicated of anything that can be identified with that term.’  Nothing was there said (as nothing was needed) of the relations that might be implied in the predication.  But now that it comes to the ultimate validity of predication, we must be clear as to what these relations are; and it will also be convenient to speak no longer of terms, as in Formal Logic, but of the things denoted.  What relations, then, can be determined between concrete facts or phenomena (physical or mental) with the greatest certainty of general truth; and what axioms are there that sanction mediate inferences concerning those relations?