According to the definition of textbooks, propositions without logical conjunctions "or" and "not" are called simple propositions (those with logical books are called atomic propositions). It is considered that simple proposition is the most basic unit of logical calculus and should be regarded as an inseparable whole. For example, "3 is the divisor of 12" and "0.5 is an integer" are all simple.

A proposition composed of simple propositions and logical conjunctions is a compound proposition. For example, "20 is divisible by 4 or 5", "the opposite sides of a parallelogram are equal and parallel" and "2 is a non-prime number" are all compound propositions because they contain logical conjunctions or and respectively.