Validity, Inference and Implicatures I

Abstract

Dr. Bunge contested the validity of (1) Q /∴ if P then Q and (2) P /∴ P or Q. His reasons against these arguments are confused. According to him, (a) if the conclusion of an argument is not relevant (for a particular discourse, I assume), then the argument is invalid; (b) if (1) were valid and P referred to an object, Q would refer to it (this is why, in Bunge’s opinion, some physicists think that certain propositions of physical theory refer to the observer; if this were so, those physicists could have concluded that any proposition could be about anything; (c) the validity of (1) has been seriously defended when “if … then …” is interpreted in a strong sense that cannot be defined by the truth-table (e.g., it is sufficient for Q that P).

Simpson defended the validity of (2) from an objection of Strawson. The point was that the conclusion expresses a doubt not expressed by the premiss. Simpson understands “or” as “v” and has a clear idea of what “validity” means in logic. So, he concludes that the argument is valid. Then, he tries to show what is wrong with Strawson’s objection. He thinks that the argument is logically valid but psychologically implausible, A valid argument and a psychological inference are not the same thing. But this distinction does not prove that Strawson’s objection is incorrect, since it fails to show that P or Q can be true when the speaker does not have the doubt expressed by the sentence, and so, that it can be true when P is true, and the speaker knows it, In fact, the solution to this problem is to be found in Grice’s theory of conversational implicatures. Another problem with Simpson’s solution is that it implies a false relation between valid argument and the process of change of beliefs called inference, This wrong idea is that a good inference is a valid argument with certain extra conditions. In a second part of this article Harman’s ideas about inference and valid argument will he discussed.

The article tries to explain what the meaning of “valid” is when applied to a natural language, and what the role of Grice’s theory of conversational implicatures is in the explanation of verbal behaviour and of the speaker’s intuitions.

[Summary by Hugo Margáin]