Quintilian Institutio Oratoria 7.8

[1] The syllogistic basis ¹ has some resemblance to the basis concerned with the letter and intention of the law, since whenever it comes into play, one party rests his case on the letter: there is, however, this difference between the two bases, that in the latter we argue against the letter, in the present beyond the letter, while in the latter the party defending the letter aims at securing that in any case the letter may be carried into effect, whereas in the present his aim will be to prevent anything except the letter being carried into effect. The syllogism is sometimes employed in conjunction with definition: for often if the definition be weak it takes refuge in the syllogism. Assume a law to run as follows: The strongest line for the accuser to take will be to assert that the love-potion was a poison. This involves definition. If it proves weak, we shall have recourse to the syllogism, to which we shall proceed after virtually dropping our previous argument, and which we shall employ to decide the question whether she does not deserve to be punished for administering the lovepotion no less than if she had caused her husband's death by poison.

[3] The syllogistic basis, then, deduces from the letter of the law that which is uncertain; and since this conclusion is arrived at by reason, the basis is called ratiocinative. ² It may be subdivided into the following species of question. If it is right to do a thing once, is it right to do it often? Example: If the law grants a privilege with reference to one thing, does it grant it with reference to a number? Example:

[4] If a thing is legal before a certain occurrence, is it legal after it? Example: ³ Is that which is lawful with regard to the whole, lawful with regard to a part? Example: Is that which is lawful with regard to a part, lawful with regard to the whole? Example:

[5] In all these cases the syllogism rests on the letter of the law as well: for the accuser urges that the provisions of the law are precise. He will say, or or and so on.

[6] But to this we may reply, Thus we infer what is doubtful from what is certain. It is a more difficult task to deduce from the letter of the law that which is not actually prescribed by the letter, and to argue because that is the case, so also is this. Take the following problems. or

[7] Under this heading come questions such as the following: if there is not a special law applicable to the case, ought we to have recourse to an analogous law? is the point in question similar to what is contained in the letter of the law? Now it should be noted that what is similar may be greater, equal or less. In the first ease we enquire whether the provisions of the law are sufficient, or, if they are insufficient, whether we should have recourse to this other law. In both cases it is a question of the intention of the legislator. But the most effective form of treatment in such cases will be to appeal to equity.