A propositional attitude is the way in which a subject behaves compared to a Proposition. The propositional attitudes most current are " to believe that p" , " to say that p" , " to think that p" , " to wish that p" etc, where p is the proposal which raw, known as, is thought or wished.

General presentation

The propositional attitudes are a subject of study of the philosophy of logic since creation with Frege and Russell of the Logique mathematics. This one obeys a rule which is the principle of substitution. This principle affirms that two proposals which have the same value of truth can be substituted one for the other without changing the Valeur of truth of the general proposal which contains them. Since Leibniz one says that one can replace them salva veritate , i.e. by preserving their value of truth. Thus, if " p" " q" and " r" are proposals, and if p and Q have the same value of truth, then the " proposal; p & r" the same value of truth will have as " Q & r".

However, this principle seems to be contradicted by the propositional attitudes. That is to say Paul an unspecified individual. Paul believes that Stendhal wrote the red and the black . However, under the terms of the substitution of the identical ones, since Stendhal is the same man as Henri Beyle, then it should be true that Paul believes that Henri Beyle wrote the red and the black . However, it is not necessarily true, because Paul can be unaware of that Stendhal is Henri Beyle. Thus there exist certain situations where the rules of traditional logics are not worth any more. In a belief, it is necessary to take account of the knowledge of the subject to determine which are substitutions which would change the value of truth and those which would not do it. One sees very clearly in the substitution of " Oedipus wants to marry Jocaste " with " Oedipus wants to marry his mère" that a substitution of an expression by another however identical can change the significance of the proposal completely and lead to an obvious contradiction.

One qualifies the propositional of contexts not extensionnels or opaque attitudes according to the formula of Quine, because the truth of the proposals of the form " Paul believes that p" is not function of the value of truth of the elements of this proposal. The quotations are also contexts not extensionnels.

See too

• Of the denotation
• Logical mathematics