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).