The prominent American sociologist Robert King Merton passed away on February 23, 2003, in New York. He was close to turning 93, on July 4, the day of the independence of the United States, a date that the sociologist specifies in a reflection of his learning life. On the occasion of his death, it is opportune to refer to his contribution to the development of Sociology. The search for the features that identify him as a contemporary classic and that remind him as one of the pillars of 20th century sociology is done on the basis of his concept of "opportunity structure" that he not only described, but deciphered in relation to with your experience. Merton conceives the discipline of sociology as the science that aims to discover the ways in which attitudes and the paths taken by human beings are influenced, not determined in all their details, by motives grounded in social and cultural structures. It is the structures that mark the behavior of the social doctors and guide them in pre-established directions, without this meaning that there is a single destiny or that it is inexorable or that it is imposed in an unalterable way or that it violates individual options. It only means that they weigh in the decisions and that they exert a force in the subjective determinations. Faced with them, individuals can choose between alternatives through the use of free will and the use in their favor of the circumstances that are conducive to them. The structures, which have a probabilistic form, are presented as coincidences in the conduct of everyday life.