To raise the question of how either psychological or neuro-biological findings are interpreted is to assert that they do lend themselves to various modes of understanding and that these modes may hinge on often unnoted presuppositions. There are always presuppositions—preliminary interpretations—which guide and limit therapy or research, and these, in part, always function as tacit assumptions. The way in which tacit assumptions affect research is, of course, hidden. The obverse—the way in which a crucial experiment puts an end to speculation, delimits interpretation, and directs further research—is easy to see. In the latter case, experiments are designed to test consciously formulated alternative possibilities. In the case of tacit assumptions, the scientific ideal would be for them to be made