Rational Psychology

PREFACE

—[percep]tible, and we have clearly shown what harmonic changes in the body correspond to individual changes in the soul. By a deliberate plan, we have made the theory of which we spoke independent of the hypotheses of philosophers concerning the union of the soul with the body; for since those hypotheses are subject to disputes, it seemed poorly advised to involve our theory in the quarrels of others. To that end, we have openly taught that, while our theory remains intact, you may give whatever name you wish to the hypothesis.

Three hypotheses of philosophers are celebrated today, devised for the sake of explaining the interaction interaction: the Latin "commercium" refers to the "commerce" or communication between the soul and body which occurs between the soul and the body: namely, the system of physical influx, occasional causes, and pre-established harmony.

Wolff refers to the three major 18th-century explanations for the mind-body problem:
1. Physical Influx: The soul and body directly exert force on each other.
2. Occasional Causes: God intervenes to produce a change in the soul whenever the body changes, and vice-versa.
3. Pre-established Harmony: God synchronized soul and body at creation like two perfect clocks, so they agree without interacting.

I have faithfully set forth each of these, so that they might be easily understood by all. Concerning each, I have stated my opinion without bias original: "citra partium studium," literally "without the zeal of parties", leaving it free for everyone to decide to which one they wish to grant their assent. For it matters little to me what is established concerning the cause of the interaction of the soul with the body.

Although this entire part of Psychology might seem hypothetical, and was for that very reason [separated] from Empirical Psychology Empirical Psychology: the branch of psychology based on observation and experience, rather than pure reasoning—