The Rules of the Syllogism state that in order for a Syllogism to be a _perfect_ Syllogism, it is necessary: I. _That there should be three, and no more than three, Propositions._ These three propositions are: (1) the _Conclusion_, or thing to be proved; and (2 and 3) the Premises, or the means of proving the Conclusion, and which are called the Major Premise and Minor Premise, respectively. We may understand this more clearly if we will examine the following example: _Major Premise_: "Man is mortal;" (or "A is B"). _Minor Premise_: "Socrates is a man;" (or "C is A"). Therefore: _Conclusion_: "Socrates is mortal" (or "C is B"). It will be seen that the above Syllogism, whether expressed in words or symbols, is logically valid, because the conclusion must logically follow the premises. And, in this case, the premises being true, it must follow that the conclusion is true. Whately says: "A Syllogism is said to be valid when the conclusion logically follows from the premises; if the conclusion does not so follow, the Syllogism is invalid and constitutes a Fallacy, if the error deceives the reasoner himself; but if it is advanced with the idea of deceiving others it constitutes a Sophism." The reason for Rule I is that only three propositions--a Major Premise, a Minor Premise, and a Conclusion--are needed to form a Syllogism. If we have more than _three_ propositions, then we must have more than two premises from which to draw one conclusion. The presence of more than two premises would result in the formation of two or more Syllogisms, or else in the failure to form a Syllogism. II. _That there should be three and no more than three Terms._ These Terms are (1) The Predicate of the Conclusion; (2) the Subject of the Conclusion; and (3) the Middle Term which must occur in both premises, being the connecting link in bringing the two other Terms together in the Conclusion. The _Predicate of the Conclusion_ is called the _Major_ Term, because it is the greatest in extension compared with its fellow terms. The _Subject of the Conclusion_ is called the _Minor_ Term because it is the smallest in extension compared with its fellow terms. The Major and Minor Terms are called the _Extremes_. The Middle Term operates between the two Extremes. The _Major Term_ and the _Middle Term_ must appear in the _Major Premise_. The _Minor Term_ and the _Middle Term_ must appear in the _Minor Premise_. The _Minor Term_ and the _Major Term_ must appear in the _Conclusion_. Thus we see that _The Major Term_ must be the Predicate of the Conclusion; the _Minor Term_ the Subject of the Conclusion; the _Middle Term_ may be the Subject or Predicate _of either of the premises_, but _must always be found once in both premises_. The following example will show this arrangement more clearly: