Thomas on Fallacies (3)

(N.B. Translator exercised a heavy editorial hand)

Chapter 14

Ignoratio Elenchi

The fallacy of ignoratio elenchi. “Elenchus” is a contradictory syllogism that is in one way unified and in another way divided. It is one when it concludes the contradictory of another proposition given previously, as if one were to grant an animal is incorruptible and then proceed thus:

Every composite from contraries is corruptible
Every animal is such
So every animal is corruptible

The conclusion contradicts the proposition that was granted. Two syllogisms constitute an elenchus by having contradictory conclusions, as when we add another syllogism like this:

No blessed thing is corruptible
Some animals are blessed
So some animal is not corruptible.

Because contradictory syllogism is the definition of elenchus, whatever is contrary to the definition of a contradictory syllogism excludes elenchus. So when any defect in a syllogism happens because it omits something of the definition of a syllogism and of contradiction it is, as a general principle, reduced to ignoratio elenchi.

But since contradiction is in the definition of elenchus as a difference constituting a species, it is specifically the omission of things required for contradiction that constitute ignoratio elenchi. Because a fallacy cannot happen if it fails to appear true, it is necessary… that the contradiction be apparent though lacking something necessary for a true contradiction.

A true contradiction cannot arise except with respect to one and the same thing, if not, it seems to not be a contradiction, as here:

Man runs
A donkey does not run.

Real contradictions cannot arise except from one and the same thing, while fallacy arises from the failure of someone to notice what is required for contradiction. Contradiction is the opposition of not just one and the same thing, but of the thing and the name being the same at the same time, and ignoratio elenchi is a defect arising from not noticing [this]… what causes the fallacy to appear genuine is the similitude of a deficient and perfect contradiction, and the cause of its not being so is the diversity of the same. This fallacy has four modes:

1.) A mistake taking the same thing relative to the same. As here:

Two is the double of one,
But Two is not the double of three
Therefore two is both double and not double.

This doesn’t follow since it omits that what is not made with respect to the same thing is not a contradiction.

2.) Not taking this particular in the same sense, as here

This is double in length
And this same this is also double in breadth
So one and the same thing is double and not double.

This does not follow because it fails to notice that contradiction requires that this particular be taken in the same sense.

3.) Not taking the thing “in the same way”. As here

The heavens move circularly
The heavens do not move up and down
Therefore, the heavens both move and do not move.

This does not follow because of the omission of the qualification “in the same way” which takes away the contradiction.

4.) Not taking the particular in one and the same time, as here:

The house is closed at night
The house is not closed during the day,
Therefore it is closed and not closed.

This doesn’t follow since contradiction is blocked by the diversity of time.

Notice that this fallacy beings with the fallacy of secundum quid and simpliciter since both proceed from what is said with some qualification to what is said simpliciter. There is nevertheless a difference since in secundum quid and simpliciter the qualification diminishes the ratio of what exists simpliciter, though this does not necessarily happen in this fallacy – rather the added qualifications remove the ratio of contradiction – for it would certainly follow:

This thing is double X in breadth
Therefore it is double X.

And it would not follow that there was a contradiction when referred to both things. It is also clear that that ignoratio elenchi arises from the contradiction of beings in general, which is an opposition, and the source of contradiction.

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