In the context of the concept of determinate chaos, introduced in psychology in the nineties, a modified stimulus-response formula is suggested which deals with the probabilistic predictions of responses of animate systems (brainless animate systems, animals, human persons) on stimuli. The suggested formula is used here in elaboration of a model describing the relationship among thoughts, feelings, and actions. In the framework of the model, a Darwin-like selection of behavioral and mental responses on stimuli is realized which is influenced by feelings. Transformations of human persons into mentally unhealthy states are discussed with the help of representations of the elaborated model. The model invites empirical test.