Elsewhere he refers to "my theories of historical determinism", defining the latter: "By a deterministic relationship among cultural phenomena, I mean merely that similar variables under similar conditions tend to give rise to similar consequences." The use of "tends to" implies some degree of freedom to happen or not happen, but in strict determinism, given certain causes, the result and only that result must occur. Different philosophers, however, use determinism in different senses. The deterministic element that Harris sees is lack of human social engineering: "free will and moral choice have had virtually no significant effect upon the direction taken thus far by evolving systems of social life."