1. A dialect is a particular form or derivative of a language that can vary greatly from the main language so as to be mutually unintelligible. The line between dialect and language is plastic depending on the political status of the dialect's speakers (see Cantonese). If you aren't sure, here's a good rule of thumb: A language is a dialect with an army and navy.
Lallans Speaker: Scots kythed for the first time in leeterar furm in the mids o the 14t century an didna differ muckle fae ither northren Inglis byleids.
English Speaker: I'm sorry, your dialect is completely unintelligible. It's like it wasn't actually English or something...oh.