© 2009 *KnowledgeToTheMax*

**Logic**

A model is a
procedure for making inferences. An inference may
be “correct” or “incorrect”; ideally, a model makes only correct inferences. To
ensure that this happens, the builder of a model needs principles that
discriminate correct from incorrect inferences. Logic postulates the existence
of these principles.

The
principles that discriminate are called “the principles of reasoning.”
Logic is the science of these principles.

In the
branch of logic called the “deductive” logic, it is axiomatic that every
proposition has a variable which is called its “truth-value”; the value of the
truth-value is *true* or it is *false*. In reality, though, one observes
that a proposition may be neither *true*
nor *false* but rather may be *true* in a proportion of instances in
which it is asserted lying between 0% and 100%; thid
proportion is called the “probability” of the proposition. The deductive logic
may be generalized to conform to this reality by replacement of the axiom that
every proposition has a true-value by the axiom that every proposition has a
probability; this generalization produces the so-called “probabilistic” logic.
Strong evidence supports the contention that logic and the probabilistic logic
are equivalent.