MOOD.
These distinctions of syllogism, accord. ing to figure and mood, respect chiefly simple syllogisms, or those limited to three propositions, all simple; and where the extremes and middle term are con nected immediately together. But as the mind is not tied down to any one form of reasoning, but sometimes makes use of more, sometimes of fewer premises, and often takes in compound and conditional propositions, there hence arises other dis tinctions of syllogisms.
When in any syllogism the major is a conditional proposition, the syllogism it self is termed conditional. Such is the following one : If there is a God, he ought to be wor shipped ; But there is a God : Therefore he ought to be worshipped.
In syllogisms of this kind, the relation between the antecedent, or the condition al part, " if there is a God," and the con sequent, " he ought to be worshipped," most ever be real and true ; that is, the antecedent must always contain some certain and genuine condition, which ne cessarily implies the consequent ; other wise the proposition itself will be false, and therefore ought not to be admitted into our reasonings. There are two kinds of conditional syllogisms, one of which is called in the schools modus ponens ; be cause from the admission of the antece dent they argue to the admission of the consequent, as in the syllogism above : the other is called modus tollens, because in it both antecedent and consequent are rejected, as in the following syllogism : If God were not a being of infinite goodness, neither would he consult the happiness of his creatures ; But God does consult the happiness of his creatures ; Therefore he is a being of infinite good ness.
Again, as from the major's being a conditional proposition, we obtain condi tional syllogisms; so, where it is a dis junctive proposition, the syllogism is also called disjunctive, as in the following ample: The world is either self-existent, or the Work of some finite, or some infinite being.
But it is not seliexistent, nor the work of a finite being : Therefore it is the work of an infinite being.
Now a disjunctive proposition is that, where, of several predicates, we affirm one necessarily to belong to the subject, to the exclusion of all the rest, but leave that particular one undetermined ; hence it follows, that as soon as we determine the particular predicate, all the rest are to be of course rejected ; or if we reject all the predicates but one, that one neces sarily takes place. When, therefore, in a disjunctive syllogism, the several pre dicates are enumerated in the major, if the minor establishes any one of these predicates, the conclusion ought to re move all the rest ; or if, in the minor, all the predicates but one are removed, the conclusion must necessarily establish that one.
In the several kinds of syllogisms hi therto mentioned, we may observe, that the parts are complete ; that is, the three propositions of which they consist are expressed in form. But it often happens, that some one of these premises is not only an evident truth, but also familiar, and in the mouths of all in which case it is usually omitted, whereby we have an imperfect syllogism, that seems to be made up of only two propositions : such is the following one : Every man is mortal ; Therefore every king is mortal.
Here the minor proposition, "every king is man," is omitted, as being so clear and evident, that the reader may easily sup ply it.