A symbol that looks like an upside down A, read as "for all," "for every," "for each," or "for any."
Existential Quantifier
A symbol that looks like a backward E, read as "there exists one," "for at least one," or "for some."
Predicate Well-formed Formulas (wffs)
wffs containing predicates and quantifiers.
Scope
"Grouping symbols" such as parentheses and brackets that identify the section of the well-formed formula (wff) to which the quantifier applies.
Free Variable
A variable that occurs somewhere is a well-formed formula (wff) where it is not part of a quantifier and is not within the scope of a quantifier involving that variable.
Valid
Such as for a well-formed formula (wff) it it is True in all possible interpretations.