To a legitimate syllogism it is essential that there should be three, and no more than three, propositions, namely, the conclusion, or proposition to be proved, and two other propositions which together prove it, and which are called the premisses. It is essential that there should be three, and no more than three, terms, namely, the subject and predicate of the conclusion, and another called the middleterm, which must be found in both premisses, since it is by means of it that the other two terms are to be connected together. The predicate of the conclusion is called the major term of the syllogism; the subject of the conclusion is called the minor term. As there can be but three terms, the major and minor terms must each be found in one, and only one, of the premisses, together with the middleterm which is in them both. The premiss which contains the middleterm and the major term is called the major premiss; that which contains the middle term and the minor term is called the minor premiss. Syllogisms are divided by some logicians into three _figures_, by others into four, according to the position of the middleterm, which may either be the subject in both premisses, the predicate in both, or the subject in one and the predicate in the other. The most common case is that in which the middleterm is the subject of the major premiss and the predicate of the minor. This is reckoned as the first figure. When the middleterm is the predicate in both premisses, the syllogism belongs to the second figure; when it is the subject in both, to the third. In the fourth figure the middleterm is the subject of the minor premiss and the predicate of the major. Those writers who reckon no more than three figures, include this case in the first. Each figure is divided into _modes_, according to what are called the _quantity_ and _quality_ of the propositions, that is, according as they are universal or particular, affirmative or negative. The following are examples of all the legitimate modes, that is, all those in which the conclusion correctly follows from the premisses. A is the minor term, C the major, B the middleterm. FIRST FIGURE. All B is C No B is C All B is C No B is C All A is B All A is B Some A is B Some A is B therefore therefore therefore therefore All A is C No A is C Some A is C Some A is not C SECOND FIGURE. No C is B All C is B No C is B All C is B All A is B No A is B Some A is B Some A is not B therefore therefore therefore therefore No A is C No A is C Some A is not C Some A is not C THIRD FIGURE.