Theory of Opposites

He built off of the pre-existing Hippocratic theory of humors

Galen's Additions and Advancements

Hippocrates's school of thought mainly focused on diagnosing a disease whereas Galen's goal was treatment. He used Hippocrates's humors to develop cures for ailments.

The idea was to examine the patient's symptoms, determine which of the four humors were unbalanced, then prescribe the patient something of the opposite humor.

For example, if his patient was portraying choleric symptoms that were hot and dry he would use something moist and cold from the other end of the spectrum.

This method was rather effective.

Diagram illustrating the four humors and their associative characteristics