Train of thought

We use the expression train of thought to refer to the process of thinking about a sequence of connected ideas. We often use this expression to refer to an uninterrupted flow of ideas, or the development of a line of reasoning in our mind.

This expression can be used in formal and informal settings, and is used quite frequently in both. Although train of thought relates to the progression of one thought to another, we usually use this expression when that process has been interrupted in some way. We also use it when we want to avoid being interrupted out of fear of forgetting a good point or idea. Train of thought is often paired with the verb "lose." For example:

  • My son interrupted me while I was writing my analysis, and now I’ve lost my train of thought.
  • Sorry... what was I just saying? I got distracted by an email and lost my train of thought.

A: Do you mind if I interrupt briefly? I’d like to add a comment to the point that you just made.
B. Sure. Let me just finish my train of thought and then you can share your feedback.

Did you know? This expression was first recorded in 1651 by the philosopher Thomas Hobbes. The word "train" was used to emphasize an orderly sequence similar to train carriages that moved together, one by one, in the same direction.