The anthropic principle takes two primary forms: the weak (WAP) and the strong (SAP). The WAP is a reflective and happenstantial inquiry: The observed values of all physical and cosmological quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirement that the universe be old enough for it to have already done so. The SAP is much more problematic: rather than considering just one universe we envisage an ensemble of possible universes—among which the fundamental constants of nature vary. Sentient beings must find themselves to be located in a universe where the constants of nature (in addition to the spatiotemporal location) are congenial.
There’s actually a third anthropic principle, the Final Anthropic Principle (FAP): Intelligent, information-processing must come into existence in the universe, and, once it comes into existence, it will never die out. If scientists could ever have a sense of humor, the late Martin Gardner referred to FAP as the Completely Ridiculous Anthropic Principle (CRAP).
 John Barrow and Frank Tipler, The Anthropic Cosmological Principle (Oxford: Oxford University Press, 1986), 16.
 Roger Penrose, The Road to Reality (New York: Random House, 2004), 758-59.
 Martin Gardner, “Wap, Sap, Pap, and Fap,” New York Review of Books 23, no. 8 (May 8, 1986): 22-25.