Five-Factor Theory (FFT) provides a broad but largely blank template for causal personality research. Within FFT, there are three major categories of questions: (1) How do biological structures and functions lead to trait levels? (2) how do traits and the environment give rise to acquired psychological institutions? and (3) how do personality characteristics interact with specific situations to determine behaviors and reactions? Both practical and ethical issues complicate the search for the causes of trait change. Causal explanations of the development of characteristic adaptations are likely to be incomplete, because there are many different ways in which the same adaptation may be acquired. Studies of the determinants of behavior are usually left to social, educational, or clinical psychologists-although personality psychologists may make distinctive contributions by emphasizing the role of the individual in selecting and creating situations. A causal understanding of the functioning of the personality system is possible through the integration of many lines of evidence, but it is likely to take a very long time. In the meanwhile, personality psychologists may fruitfully pursue the identification of practical causes by which individuals with a given set of traits can optimize their adaptation. If we require truth in any strict sense, we must confine ourselves to one entire state of the world. This will be the cause, and the next entire state will be the effect. There is much truth in this conclusion, but it remains indefensible.F. H. Bradley, 1893/1966, p. 48.