train of thought
A succession of connected ideas, a path of reasoning, as in You've interrupted my train of thought; now what was I saying? This idiom, which uses train in the sense of "an orderly sequence," was first recorded in 1651, in philosopher Thomas Hobbes's Leviathan.
|train of thought|
|the connections that link the various parts of an event or argument together; "I couldn't follow his train of thought"; "he lost the thread of his argument"|