Wherefore we must find out from what has been already said, what has reference to utility; but as to what is possible to be done or not, with reference to which people usually inquire also how easily a thing can be done, and how far it is desirable that it should be done, we must consider chiefly with reference to those causes which produce each separate result.  For there are some causes which of themselves produce results, and some which only contribute to the production of a result.  Therefore, the first are called efficient causes; and the last are classed as such, that without them a thing cannot be brought about.  Again, of efficient causes, some are complete and perfect in themselves; some are accessory to, and, as it were, partners in the production of the result in question.  And of this kind the effect is very much diversified, being sometimes greater or less; so that which is the most efficacious is often called the only cause, though it is in reality but the main one.  There are also other causes which, either on account of their origin or on account of their result, are called efficient causes.  But when the question is, what is best to be done, then it is either utility or the hope of doing it which urges men’s minds to agree with the speaker.  And since we have now said enough about utility, let us speak of the means of effecting it.

XXVII.  And on this point of the subject we must consider with whom, and against whom, and at what time, and in what place we are to do such and such a thing, also what means of arms, money, allies, or those other things which relate to the doing of any particular thing we have it in our power to employ.  Nor must we consider only those means which we have, but those circumstances also which are unfavourable to us.  And if in the comparison the advantages preponderate, then we must persuade our hearers, not only that what we are advising can be effected, but we must also take care that it shall appear easy, manageable, and agreeable.  But if we are dissuading from any particular course, then we must either disparage the utility of it, or we must make the most of the difficulties of doing it, not having recourse to other rules, but to the same topics as are used when trying to persuade our hearers to anything.  And whether persuading or dissuading, the speaker must have a store of precedents, either modern, which will be the best known, or ancient, which will perhaps have the most weight.  And in this kind of discourse he must consider how he may be able often to make what is useful or necessary appear superior to what is honourable, or vice versa.  But sentiments of this kind will have great weight in influencing men’s minds, (if it is desirable to make an impression on them,) which relate either to the gratification of people’s desires, or to the glutting of hatred, or to the avenging of injury.  But if the object is to repress the feelings of the hearers, then they must be reminded of the uncertainty of fortune, of