V. Now we will set forth the topics one portion of which applies to all conjectural discussion.  But it will be desirable to take notice of this in the exposition of these topics and of all the others, and to observe that they do not all apply to every discussion.  For as every man’s name is made up of some letters, and not of every letter, so it is not every store of arguments which applies to every argumentation, but some portion which is necessary applies to each.  All conjecture, then, must be derived either from the cause of an action, or from the person, or from the case itself.

The cause of an action is divided into impulsion and ratiocination.  Impulsion is that which without thought encourages a man to act in such and such a manner, by means of producing some affection of the mind, as love, anger, melancholy, fondness for wine, or indeed anything by which the mind appears to be so affected as to be unable to examine anything with deliberation and care, and to do what it does owing to some impulse of the mind, rather than in consequence of any deliberate purpose.

But ratiocination is a diligent and careful consideration of whether we shall do anything or not do it.  And it is said to have been in operation, when the mind appears for some particular definite reason to have avoided something which ought not to have been done, or to have adopted something which ought to have been done, so that if anything is said to have been done for the sake of friendship, or of chastising an enemy, or under the influence of fear, or of a desire for glory or for money, or in short, to comprise everything under one brief general head, for the sake of retaining, or increasing, or obtaining any advantage; or, on the other hand, for the purpose of repelling, or diminishing, or avoiding any disadvantage;—­for those former things must fall under one or other of those heads, if either any inconvenience is submitted to for the purpose of avoiding any greater inconvenience, or of obtaining any more important advantage; or if any advantage is passed by for the sake of obtaining some other still greater advantage, or of avoiding some more important disadvantage.

This topic is as it were a sort of foundation of this statement of the case; for nothing that is done is approved of by any one unless some reason be shown why it has been done.  Therefore the accuser, when he says that anything has been done in compliance with some impulse, ought to exaggerate that impulse, and any other agitation or affection of the mind, with all the power of language and variety of sentiments of which he is master, and to show how great the power of love is, how great the agitation of mind which arises from anger, or from any one of those causes which he says was that which impelled any one to do anything.  And here we must take care, by an enumeration of examples of men who have done anything under the influence of similar impulse, and by a collation of similar cases, and by an explanation of the way in which the mind itself is affected, to hinder its appearing marvellous if the mind of a man has been instigated by such influence to some pernicious or criminal action.