A statement can be self-justified: S. Self-Argued Claim. This self-defense is made possible by the multi-layered semantic structure of language, and in particular by the fact that words have an orientation, which may be well grounded on implicit arguments, S. Words as arguments. Just as it can be self-justified, a statement can be self-defeated. A statement is self-defeated when it expresses a logical or material impossibility, or when it involves a pragmatic contradiction between what is said and the act of saying it.
This phenomenon is also called autophagy. Perelman defines autophagy as a contradiction arising from the fact that “the assertion of a rule or a principle is incompatible with the conditions or with the consequences of its assertion or application. Such arguments can be called autophagy. Retaliation is the argument that attacks the rule by highlighting the autophagy” (Perelman 1977, p. 72-73).
The assertion is incompatible with the fact asserted, “the very act implies what the words denies” (id. p. 73). Perhaps the best-known case of autophagy is that of the Cretan Epimenides affirming that “all the Cretans are liars”:
There are no more cannibals, we have eaten the last one.
S1 — All statements can be questioned.
S2 — I question this statement.
Retaliation is a kind of refutation reconstructing a claim as pragmatically self-defeating on the basis of its very content, and in virtue of its own principles. In philosophy, this strategy, known as the epitrope, is applied by Socrates to refute Protagoras’ thesis according to which:
Man is the measure of all things: of the things which are, that they are, and of the things which are not, that they are not. (Plato, Theaethetus, 152a; CW, p. 169)
This doctrine exhibits that “most exquisite feature” that if true, it is false:
Socrates: — […] Protagoras admits, I presume, that the contrary opinion about his own opinion (namely, that it is false) must be true, seeing he agrees that all men judge what is.
Theodorus: — Undoubtedly.
Socrates: — And in conceding the truth of the opinion of those who think him wrong, he is really admitting the falsity of his own opinion?
Theodorus: — Yes, inevitably. (Id., 171a-b; OC, p. 190)
This refutation is based on the principle of non-contradiction; to maintain consistency, a Skeptic will have to doubt this principle.