Institutio Oratoria

Before, however, I proceed to classify the various species of artificial proof, I must point out that there are certain features common to all kinds of proof. For there is no question which is not concerned either with things or persons, nor can there be any ground for argument save in connexion with matters concerning things or persons, which may be considered either by themselves or with reference to something else;

while there can be no proof except such as is derived from things consequent or things opposite, which must be sought for either in the time preceding, contemporaneous with or subsequent to the alleged fact, nor can any single thing be proved save by reference to something else which must be greater, less than or equal to it.

As regards arguments, they may be found either in the questions raised by the case, which may be considered by themselves quite apart from any connexion with individual

Again there are four forms of proof. First, we may argue that, because one thing is, another thing is not; as It is day and therefore not night. Secondly, we may argue that, because one thing is, another thing is; as The sun is risen, thereit is day. Thirdly, it may be argued that because one thing is not, another thing is; as It is not night, therefore it is day. Finally, it may be argued that, because one thing is not, another thing is not; as He is not a reasoning being, therefore he is not a man. These general remarks will suffice by way of introduction and I will now proceed to details.