Based on data derived from a study of three generations of black women in Philadelphia in 1975, the report offers a new explanation of fertility differences between generations, population subgroups, and individuals. The authors hypothesize that varying fertility patterns are due to societal norms and circumstances which influence womens' attitudes toward birth control. A survey questionnaire which was organized around events occurring in the age intervals 13-19, 20-29, and 30-49 was administered to 718 women. The questionnaire inquired about all events such as pregnancy and contraception that took place in a particular age interval before moving on to the next interval. Questions centered on fertility determinants, specifically fecundity, frequency of intercourse, marital stability, and use of birth control. Among the more pertinent findings presented are: attitude toward birth control is as important as simple knowledge of birth control methods; pregnancy can influence mating, fecundity, and contraceptive use as well as vice versa; and the timing of reproductive events, often determined by chance factors, influences fertility differentials. The conclusion is that researchers can provide a new perspective on 20th century American fertility patterns if they concentrate on the temporal dimensions of fertility determinants. (DB)