The word "phenomenology" word is often used of a philosophical "school" which originated with the work of Franz Brentano in the 19th century, and whose leading figure was Edmund Husserl.  Its general meaning is the study of phenomena, or "appearances".
 
The OED writes: "the theory, put forward by the German philosopher Edmund Husserl (1859­1938) and his followers, to the effect that the pure and transcendental nature and meaning of phenomena, and hence their real and ultimate significance, can only be apprehended subjectively; the method of reduction, based by Husserl on Descartes’s method, whereby all factual knowledge and reasoned assumptions about the phenomenon as object and the experiencing ‘ego’ are set aside so that pure intuition of the essence of the phenomenon may be rigorously analysed and studied."

But Thom applies it here less exactly to the forms of the phenomena themselves.


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