This thesis is an analysis of functionalist theories and not of functionalists themselves. I will determine what the theories cover hoping to clear up to some extent the misunderstandings and limited aspects pertaining to the theories. Functionalism is the underlying order in architecture. It embodies and synthesizes the life principle with the universal laws of science; it humanizes architecture and gives it meaning. These thoughts are constantly recurring in the writing of the functionalists, who did not disregard imagination but sought to give it order and meaning in relation to man's physical, intellectual and spiritual needs. The main lesson we can learn from the functionalists is not what they did so much as what they said. Functionalism is not an object, it is a philosophy; a basis for architecture. No one building can be held up as the perfect embodiment of functionalist principles and many (done by functionalists) are quite bad. Start with first hand knowledge rather than second hand experience; that knowledge based on inductive reason and the sense experiences. The conscious following of rules is the surest way to kill freshness. Principles should be fused into the subconscious element of our thought and become one with feeling and intuition; an integral part of our everyday experiences. The functionalists are concerned with the rational approach emphasizing the physical needs of man because this approach is easily explained and demonstrated. The metaphysical aspects of the intellect and spirit are less satisfying since it is impossible to "drive a point home" with a conclusive example. The functionalists repeatedly allude to the intellectual and spiritual needs of man but in compliance with the physical needs. The main difference between functionalism and formalism (form for form's sake) is that through functionalism expression and delight evolve in accordance with the total needs of man. Whereas formalism is an end in itself, compromising the needs of man.