A notion in logic and philosophy is a reflection in the mind of real objects and phenomena in their essential features and relations. Notions are usually described in terms of scope (sphere) and content. This is because notions are often created in response to empirical observations (or experiments) of covarying trends among variables.
However, in philosophy the term "primitive notion" has historical content. For example, Gottfried Leibniz wrote De Alphabeto Cogitationum Humanarum (English: An Alphabet for Human Thought). Jaap Maat (2004) reviewed Leibniz for Philosophical Languages of the 17th Century. According to Leibniz, "The alphabet of human thought is a catalogue of primitive notions, or those we cannot render clearer by any definitions." Maat explains, "a thing which is known without other intermediate notions can be considered to be primitive," and further, "a primitive notion is said to be conceived through itself".
Another example is in the Meditations of René Descartes:
"[Descartes'] claim that mind-body unity is a primitive notion on a par with the primitive notions of thinking and extended substance..."