be at the back of one’s mind —(also: be in the back of one’s mind) be vaguely aware of smth. that is not present in one’s conscious thoughts:
- There was at the back of his mind an idea, dimly seen at moments, never wholly comprehended.
cast one’s mind back to something—think about smth. that happened in the past, which one might not remember well:
- In order to understand these developments, it is necessary to cast back one’s mind to the social attitudes of that period.