Alcmaeon of Croton

The Life of Alcmaeon

Alcmaeon, son of Peirithous, born in the Greek city of Croton around the 5th century BC, was a pre-Socratic physician and philosopher, and according to some ancient sources, he was also one of the main disciples of Pythagoras.

Little is known about the life and thought of this philosopher, and what is known is thanks to some testimonies and fragments about him. Diogenes Laertius, states that Alcmaeon wrote mainly on subjects connected with medicine. He is said to have been the first to dissect a human body for scientific purposes.

However, there are no historical accounts of his life as a practicing physician. Aelius Galenus, for example, considered him more of a philosopher-scientist than a doctor. For this reason, some scholars argue that Alcmaeon should be more called a philosopher of physis, a line of thought followed by most of the pre-Socratics.

It is clear from the testimonies about Alcmaeon that he was a thinker interested in issues of psychology, physiology and epistemology. In the physiological realm, he investigated the nature of sleep, death and the formation of embryos.

Brain, comprehension and perception

Alcmaeon was the first Greek philosopher to consider the brain as the seat of psychic functions; he believed that the senses (sight, touch, etc.) and thought were linked to the brain.

He was also the first to distinguish understanding from perception. In one of the fragments he says:

Man differs from other beings because he is the only one who understands, while others only perceive, but do not understand.

Although animals have the senses, they are not able to gather this data captured by the senses and somehow make inferences in the same way that the human being can.

Knowledge according to Alcmaeon of Croton

Alcmaeon was not a skeptic, but he considered human knowledge to be somewhat limited compared to the knowledge of the gods.

For him, men could not have a clear knowledge about invisible things, they could only make more or less reasonable judgments through the use of sensations.

In one of the surviving fragments, Alcmaeon says:

[…] Of imperceptible things only the gods have certain knowledge; men are only permitted to conjecture.

What are such imperceptible and invisible things that only the gods know?

Some scholars, taking into account that Alcmaeon was a physician, consider that he would be referring to diseases that afflict the human body internally, diseases that leave no external signs.

The Immortality of the Soul

Alcmaeon was also one of the first thinkers to devise arguments to prove the immortality of the soul.

According to Aristotle, Alcmaeon defended the immortality of the soul, because of its resemblance to the immortal being. For him, the soul is in eternal motion. And all divine beings move eternally, for example, the moon, the sun, stars and the whole sky (Aristotle, De Anima, I, 2 405a).

It is an argument of analogy, the soul that moves eternally is like the heavenly bodies, considered by him as divine. The argument is therefore based on the premise that everything that moves eternally is immortal.


Some sources suggest that Alcmaeon also elaborated a cosmological theory. He proposed that the planets moved from west to east, in the opposite direction to the motion of the fixed stars in the sky.

In a possible connection with Anaximenes, he also held that the sun and moon were flat.


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