**The Word of the Week is**:* Existential Instantiation*

**Definition**: A rule of inference that introduces existential quantifiers. The symbol for an existential quantifier is (∃x).

**More about the term**: The existential quantifier indicates that there is at least one thing in a categorical reference. Instantiation is an operation that removes a quantifier and replaces every variable bound by the quantifier with that same instantial letter. There are eight rules of inference to derive a conclusion of an argument via deduction:

- Modus Ponens: p ⊃ q … p… .:q
- Modus Tollens: p ⊃ q … ~q … .: ~p
- Pure Hypothetical Syllogism: p ⊃ q … q ⊃ r … .: p ⊃ r
- Disjunctive Syllogism: p v q … ~q … .:p
- Constructive Dilemma: (p ⊃ q) & (r ⊃ s) … p v r … .: q v s
- Simplification: p & q… .: p
- Conjunction: p … q … .: p & q
- Addition: p … .: p v q