In the article "Cohort Effects on Non-marital Fertility," in this issue of "Social Forces," Jean Stockard employs a novel strategy for disentangling cohort, period, and age effects on the non-marital fertility ratio. In a model with fixed-effect controls for age and for time period, the author documents evidence for three cohort-specific factors affecting the non-marital birth ratio of a given cohort ages 20-44. The first is the non-marital birth ratio at the time a cohort is born. The second is the cohort percent enrolled in school at ages 18-21. The third is the cohort sex ratio at ages 20-24. In models for non-Hispanic whites, two of these cohort variables have statistically significant coefficients, and in models for non-Hispanic blacks, all three variables have statistically significant coefficients. In this comment, the author begins by describing the cohort effect on non-marital birth ratios as it is described by Stockard. Then he explains how the same observed pattern could arise from an age-period interaction. Finally, he offers two arguments that would favor the age-period interpretation over the cohort interpretation. He limits his analysis to the results for non-Hispanic whites; results for non-Hispanic blacks and their interpretation are generally analogous to the results and interpretation for non-Hispanic whites. (Contains 1 table and 4 figures.)