Inclusive-fitness models have been criticized because they give incorrect results for cases in which fitness components interact nonadditively. However, this failure is not due to anything intrinsic to the inclusive-fitness viewpoint. It stems from an essentially quantitative genetic feature of the model, an attempt to separate fitness terms from genetic terms. A general rule is provided for determining when such a separation is justified. This rule is used to show how Price's covariance equation is related to standard quantitative genetic results and to derive quantitative genetic equations for inclusive fitness and group selection. It also shows that the group-selection model is no more general than the inclusive-fitness viewpoint. These models serve a role that is different from, but not inferior to, population-genetics models. Although they are less exact under some conditions, like quantitative genetic models in general, they provide us with measurable parameters.