Train of thought

The train of thought or track of thought refers to the interconnection in the sequence of ideas expressed during a connected discourse or thought, as well as the sequence itself, especially in discussion how this sequence leads from one idea to another.
When a reader or listener "loses the train of thought", comprehension is lost of the expressed or unexpressed thought.
The term "train of thoughts" was introduced and elaborated as early as in 1651 by Thomas Hobbes in his Leviathan, though with a somewhat different meaning :