# Definition:Basic WFF of Predicate Logic

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## Definition

Let $\LL$ be the language of predicate logic.

A WFF $\mathbf A$ of $\LL$ is called **basic** if and only if it does not start with a logical connective.

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**Basic WFFs** are useful to consider as atoms when analysing propositional logic within the larger context of predicate logic.

Expressed more formally, we can take the **basic WFFs** as the vocabulary of the language of propositional logic.

Do note that e.g. $\forall x: x = x \land x = x$ is considered **basic** even though it contains the logical connective $\land$.

This is because $\land$ is not the main connective.

## Also see

## Sources

- 2009: Kenneth Kunen:
*The Foundations of Mathematics*... (previous) ... (next): $\text{II}.9$ Tautologies: Definition $\text{II}.9.1$