Fama is most often thought of as the father of efficient market hypothesis, beginning with his Ph.D. thesis. In a ground-breaking article in the May, 1970 issue of the Journal of Finance, entitled “Efficient Capital Markets: A Review of Theory and Empirical Work,” Fama proposed two crucial concepts that have defined the conversation on efficient markets ever since.
First, Fama proposed three types of efficiency: (i) strong-form; (ii) semi-strong form; and (iii) weak efficiency. Second, Fama demonstrated that the notion of market efficiency could not be rejected without an accompanying rejection of the model of market equilibrium (e.g. the price setting mechanism). This concept, known as the “joint hypothesis problem”.
Full text of this masterpiece: Fama_Efficient Capital Markets: A Review of Theory and Empirical Work (.pdf