Weinreich's story about it, per Wikipedia
A teacher at a Bronx high school once appeared among the auditors. He had come to America as a child and the entire time had never heard that Yiddish had a history and could also serve for higher matters.... Once after a lecture he approached me and asked, 'What is the difference between a dialect and language?' I thought that the maskilic contempt had affected him, and tried to lead him to the right path, but he interrupted me: 'I know that, but I will give you a better definition. A language is a dialect with an army and navy.' From that very time I made sure to remember that I must convey this wonderful formulation of the social plight of Yiddish to a large audience.
