These nouns refer to what is formed or represented in the mind as the product of mental activity.
- Idea has the widest range:
.."Human history is in essence a history of ideas" (H.G. Wells).
- Thought is distinctively intellectual and stresses contemplation and reasoning:
.. "Language is the dress of thought" (Samuel Johnson).
- Notion often refers to a vague, general, or even fanciful idea:
.. "She certainly has some notion of drawing" (Rudyard Kipling).
- Concept and conception are applied to mental formulations on a broad scale:
.. You seem to have absolutely no concept of time.
.. "Every succeeding scientific discovery makes greater nonsense of old-time conceptions of sovereignty" (Anthony Eden).