ABSTRACT
One of the most outstanding characteristics of the human mind is its capacity to draw valid inferences from verbally expressed statements. This deductive component of human thought (Wason & Johnson-Laird, 1972) is best illustrated by the competent behavior of those who by the analysis of formal reasoning have made logic a science. However, this capacity is also to be found in those who, though having not received formal training, are nevertheless up to solving deductive problems according to the principles of logic (albeit perhaps only in certain, determined circumstances). There are then two circumstances that allow us to speak of a human capacity for deductive thought, one that we could identify with logic itself and its 2000 years old traditions; and another, which has more to do with the acts of the untrained as studied in the psychology of reasoning (which has but a mere 100 years to its name). It is no wonder then that the first, logic, has been and still is of great importance in the development
of psychological theories that seek to explain those mechanisms that underlie human deductive behavior.
