Idea, the principal term in Spinoza’s epistemology, is an indirect mode for the attribute of thought. Idea is a primary, active, and judgmental constituent of the human soul. Different kinds of idea entail: imagination, reasoning, and intuition. Having the same meaning, truth and adequacy are the criteria of its validity. Correspondence is an extrinsic mark of the truth of idea and explanation, whereas, evidence, clearness, and distinctness are the intrinsic marks of the adequacy of the idea. According to Spinoza, knowledge is divided to two kinds, complete knowledge and incomplete knowledge, the common feature of which is "justified belief". So knowledge is a belief (an idea with judgment) which has a justification (causal explanation or sensory evidence). Therefore, imagination, reasoning, and intuition are from the category of knowledge, however, only the second and the third are regarded as complete knowledge.