Introduction to Logic

If an author writes “Q because P,” how can we tell whether he intends to explain or to persuade? We can ask: What is the status of Q in that context? Is Q a proposition whose truth needs to be established or confirmed? In that case, “because P” is probably offering a premise in its support; “Q because P” is in that instance an argument. Or is Q a proposition whose truth is known, or at least not in doubt in that context? In that case, “because P” is probably offering some account of why Q has come to be true; “Q because P” is in that instance an explanation.

Arguments that depend on rhetorical questions are always suspect. Because the question is neither true nor false, it may be serving as a device to suggest the truth of some proposition while avoiding responsibility for asserting it. That proposition is likely to be dubious, and it may in fact be false.

Questions can serve most effectively as premises when the answers assumed really do seem to be clear and inescapable. In such cases the readers (or hearers) are led to provide the apparently evident answers for themselves, thus augmenting the persuasiveness of the argument.

an interrogative sentence can serve as a premise when its question is —that is, when it suggests or assumes an answer that is made to serve as the premise of an argument.

In real life, context is critical

An argument is not merely a collection of propositions; it is a cluster with a structure that captures or exhibits some inference. We describe this structure with the terms conclusion and premise. The of an argument is the proposition that is affirmed on the basis of the other propositions of the argument. Those other propositions, which are affirmed (or assumed) as providing support for the conclusion, are the of the argument.

However, the concept of a proposition is seen by many as making a useful distinction between a sentence and what the sentence asserts. Consequently, in this book we use both terms.

Proposition is the term we use to refer to what it is that declarative sentences are typically used to assert.

It is raining.