The propositional calculus is based on statements which have truth values ( true or false).
The calculus provides a means of determining the truth values associated with statements formed from ``atomic'' statements. An example:
If p stands for ``fred is rich'' and q for ``fred is tall'' then
we may form statements such as:
Note that 
, 
, 
and 
are all binary connectives. They are sometimes referred to, respectively, as the
symbols for disjunction, conjunction, implication and equivalence.
Also, 
is unary and is the symbol for negation.
If propositional logic is to provide us with the means to assess the truth value of compound statements from the truth values of the `building blocks' then we need some rules for how to do this.
For example, the calculus states that p
q is true
if either p is true or q is true (or both are true).
Similar rules apply for all the ways in which the building blocks can be combined.