The concept (notion) is “the basic element of thinking by which is reflected what is essential and general in
objects and phenomena, as well the essential relations between them”. It is “a mental scheme with which our
thinking operates at a superior plan”. “The concept reflects the similarities between objects, situations and events
which are rather different” (Bogdan and Stănculescu, 1970, p. 157). The concepts “does not ever present isolated in
our thinking, but always under the form of systems of notions, whose ensemble makes up the fundamentals of
science” (Bogdan and Stănculescu, 1970, p. 100).