Full Idea
If the man who invented bifocals was the first Postmaster General of the United States - that they were one and the same - it's contingently true. …So when you make identity statements using descriptions, that can be a contingent fact.
Clarification
Benjamin Franklin is the man in question
Gist of Idea
Identity statements can be contingent if they rely on descriptions
Source
Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 2)
Book Reference
Kripke,Saul: 'Naming and Necessity' [Blackwell 1980], p.98