Temperament is the dynamic-energetic dimension of personality which is best expressed through behavior. It is considered by some psychologists to be characterized by the form of our manifestations and because of that it can be defined as the formal aspect of affectivity and motor reactivity typical for one person. The very first attempt to identify and explain temperamental types belongs to ancient doctors such as Hippocrates and Galenus. They have considered, as predominant in one's body the presence of one of the four "humors": blood, lymph, yellow bile and black bile, determine the temperament. There are four types of temperament based on them: sanguine, phlegmatic, choleric and melancholic respectively.

Sanguine are lively, happy, optimistic and they adjust very easily to mostly any type of situation. Being an active person, he can change his activities very often because he is in permanent need for something new. His emotional life is very intense, but has superficial and unstable feelings. He can very easily forget about his failures or the act of being deceived by others, and can relate very easily with other people.

The phlegmatic is calm, quiet, cannot be bothered. He is very calculated in his actions, and seems to have endless patience. He also has a lot of work power and is very meticulous in every little thing that he does. As he is quite introvert, he keeps it to himself and does not communicate much. He prefers individualist activities and works. He also has a strong will.

The choleric is energetic, anxious, impetuous and sometimes too impulsive so that he/she wastes his/her own energy. This temperament is unequally manifested. Thus, moods change rapidly. This type has domination tendencies and can give himself away passionately to one idea or one goal.

The melancholic has a very low resistance to continuous effort. He speaks very little and has difficulties in relating to others and being around people. He even has troubles adapting to society. Generally he speaks very rarely and has very few gestures to accompany his speech.

According to the Russian philosopher named Ivan Petrovici Pavlov, there is another temperament classification depending on the central nervous system's characteristics. Thus, depending on the strength of the central nervous system, we can speak of people endowed with a strong nervous system and those with a weak one. Another criterion is mobility, which refers to the easiness in passing from inhibition and the other way round, depending on exterior demands. If this passing is done easily and with very little effort, we can speak of a mobile central nervous system; if it is done at a slower pace, we can speak of an inert central nervous system. The third criterion according to Pavlov refers to equilibrium, to balance. If there is a balance between excitation and inhibition, we can say that the nervous system of a person is well-balanced.

Out of mixing up these above-mentioned traits, there are four types of nervous systems. The first one belongs to the strong-unbalanced-excitable type, which is correlated to the choleric temperament type. The second one is the strong-balanced-mobile, associated to the sanguine. The third one is the strong-balanced-inert, associated to the phlegmatic, and last but not least, the fourth one is the weak type, correlated with the melancholy temperament.

The Swiss psychiatrist Carl Gustav Jung had discovered, based on some clinical experiments, that apart from individual differences, there are also typical differences. Some people are primarily oriented on the world outside themselves, and these are called extroverts, whereas others are focused on their inner life and are called introverts.

The extroverts are open, sociable, full of good will, optimistic and serene. Whether they quarrel or not with those around them, they usually don't break relationships easily. The introverts on the other hand, are rather non-communicative, hard to understand, shy. They are prone to daydreaming and have difficulties adjusting to new situations.

The English psychologist Hans Eysenck reconsidered Jung's above-mentioned distinction, amplifying the probatory casuistics, but adding a new dimension called degree of neurosis. This expresses the subject's emotional stability or instability. Eysenck has represented the two dimensions on two perpendicular axes, thus obtaining the types as follows: extrovert-stable; extrovert-unstable; introvert-stable and introvert-unstable, which he associated with the four classic temperaments (sanguine, choleric phlegmatic and melancholic).