The thinking type has a predominant thinking function. This individual considers the world in a rational way. He or she analyses things according to the laws of aristotelian logic, and evaluates them using "objective" criteria. He tends to categorise the phenomena of his environment. He is good at giving or receiving criticism, drawing conclusions or finding evidence.

Viewed astrologically this function is reflected in the air signs Gemini, Libra and Aquarius. Liz Greene points out in Relating that the air element is the only one which is not represented by animal symbols in the zodiac. Gemini and Aquarius are human symbols, and Libra an objective measuring instrument. She writes:

Air is the element which is most typically human, the furthest removed from instinctual nature; and it is the human kingdom which has developed or perhaps overdeveloped in the last two hundred years the function of thinking as its great gift.

If in a horoscope more than one planet and / or the ascendant are in air signs, the individual will perceive his environment mainly through the reasoning mind. He is interested in "reasoned" discussion, not in feelings. With a predominance of air, the feeling function often remains "underdeveloped". He might find it hard to decide "on a gut level" or to accept subjective criteria. There can be difficulties in showing emotions or reacting emotionally.

It is important to emphasise that no function is in itself better than any other. All four types have qualities which are necessary for a holistic perception and evaluation of the world. An overdeveloped thinking function which ignores the other functions, leads to emotional coldness, lack of imagination and top-heaviness.