_Composition of a Syllogism._--Every syllogism contains three propositions, of which two state the grounds or reasons, and are called the premises, the other states the inference from those positions, and is called the conclusion. These three propositions contain three, and only three, distinct terms, of which one is common to both premises, and is called the _middle_ term; the others are the extremes, one of which is the subject of the conclusion, and is called the _minor_ term; the other the predicate of the conclusion, and is called the _major_ term, from the fact that it denotes the class to which the subject or minor term belongs. In the syllogism,--Every man is mortal; Socrates is a man; therefore, Socrates is mortal,--the three terms are, man, mortal, and Socrates: of these, Socrates, or the subject of the conclusion, is the minor; mortal, or the predicate of the conclusion, is the major; and man, with which both the others are compared, is the middle term. _Major and minor Premiss._--The premiss which contains the _major_ term, and compares it with the middle, is called the _major premiss_; that which, in like manner, compares the _minor_ term with the middle, is called the _minor premiss_. In the syllogism already given, 'Every man is mortal' is the major premiss; 'Socrates is a man' is the minor premiss. _The Order variable._--The order of the terms in the respective propositions, and even the order of the propositions themselves, is not invariable, but depends on circumstances. In the above proposition, it is immaterial whether I say, Every man is mortal, or, Mortal is every man; it is immaterial whether I state first the major or the minor premiss; nay, it is allowable even to state the conclusion first, and then the grounds and reasons for the same. III. LAWS OF SYLLOGISM. The following rules or maxims will be found applicable to all cases, and may be regarded as laws of the syllogism. _Middle Term unequivocal._--_The middle term must not be equivocal._--This rule is violated in the following syllogism. Nothing is heavier than lead; feathers are heavier than nothing; therefore, feathers are heavier than lead. The middle term, nothing, is here used in different senses in the two premises.