Institutio Oratoria

Quintilian

Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.

Both these

v4-6 p.245
instances are of such a nature that the argument is reversible. For it is a necessary consequence that those who could not be taken to the province against their will could not be retained against their will.

So too I feel clear that we should rank as consequential arguments those derived from facts which lend each other mutual support and are by some regarded as forming a separate kind of argument, which they [*]( Ar. Rhet. II. xxiii. 3. ) call ἐκ τῶν πρὸς ἄλληλα, arguments from things mutually related, while Cicero [*](de Inv. I. xxx. 46. ) styles them arguments drawn from things to which the same line of reasoning applies; take the following example [*](ib. 47. ) :

If it is honourable for the Rhodians to let out their harbour dues, it is honourable likewise for Hermocreon to take the contract,
or
What it is honourable to learn, it is also honourable to teach.
Such also is the fine sentence of Domitius Afer,

which has the same effect, though it is not identical in form:

I accused, you condemned.
Arguments which prove the same thing from opposites are also mutually consequential; for instance, we may argue that he who says that the world was created thereby implies that it is suffering decay, since this is the property of all created things.

There is another very similar form of argument, which consists in the inference of facts from their efficient causes or the reverse, a process known as argument from causes. The conclusion is sometimes necessary, sometimes generally without being necessarily true. For instance, a body casts a shadow in the light, and the shadow wherever it falls indicates the presence of a body.

There are other conclusions which, as I have said, are not necessary, whether as regards both cause and effect or only one of the two. For instance,

the sun colours the skin, but not
v4-6 p.247
everyone that is coloured receives that colour from the sun; a journey makes the traveller dusty, but every journey does not produce dust, nor is everyone that is dusty just come from a journey.

As examples of necessary conclusions on the other hand I may cite the following:

If wisdom makes a man good, a good man must needs be wise
; and again,
It is the part of a good man to act honourably, of a bad man to act dishonourably,
or
Those who act honourably are considered good, those who act dishonourably are considered bad men.
In these cases the conclusion is correct. On the other hand,
though exercise generally makes the body robust, not everyone who is robust is given to exercise, nor is everyone that is addicted to exercise robust. Nor again, because courage prevents our fearing death, is every man who has no fear of death to be regarded as a brave man; nor is the sun useless to man because it sometimes gives him a headache.

Arguments such as the following belong in the main to the hortative department of oratory:—

Virtue brings renown, therefore it should be pursued; but the pursuit of pleasure brings ill-repute, therefore it should be shunned.
But the warning that we should not necessarily search for the originating cause is just: an example of such error is provided by the speech of Medea [*]( The opening of Ennius' translation of the Medea of Euripides. ) beginning

Ah! would that never there in Pelion's grove,
as though her misery or guilt were due to the fact that there
  1. The beams of fir had fallen to the ground
    ;
or I might cite the words addressed by Philoctetes to Paris, [*]( From the Philoctetes of Accius, Ribbeck fr. 178. )
  1. Hadst thou been other than thou art, then I
  2. Had ne'er been plunged in woe.
v4-6 p.249
By tracing back causes on lines such as these we may arrive anywhere.