Abstract

Introducing a kind of knowledge qualified as "deaf thought", Leibniz seems to suggest a link between what he elsewhere calls blind or symbolic thought and the Lockean concept of an empty sound. This paper tries to detect reasons supporting such a comparison and to evaluate its limits. Despite the claims of his semantic theory, Locke recognizes the possibility of using words instead of ideas by mental processes which resemble, from the point of view of their cognitive set-up, the Leibnizian characterization of symbolic thought. This latter notion, however, covers a wider range of psycho-linguistic phaenomena than Locke would have allowed: substituting signs for ideas may in some cases be a source of "psittacism", but it may also provide an helpful increase in human cognitive faculties. The disagreement between the two philosophers in evaluating dangers and profits of symbolism sheds some light on their different approaches to mathematical issues.