How does astrology work? What is the force that makes astrology work?

The simple answer is we do not know. Many scientists that have dismissed astrology out of hand are swift to note that of the four forces known to classical science-strong and weak nuclear, electromagnetic, and gravitational-the only possible measurable, observable force that could be responsible for the planets to effect human affairs would be gravitational. However, the gravitational force between planets and earth is so negligible as to have no effect. The actual force of astrology may never be entirely quantifiable, however, as belief systems rapidly change and more sophisticated instruments and experimental designs evolve, science as method may become more sensitive to a force or series of forces that astrology studies.

The obstacle in believing that planets and human behavior are interrelated via force is mostly likely due to the current, but vanishing, worldview that suggests that objects have no innate relationship to each other, that action-at-a-distance or material and efficient causation is the deepest level of causation in the universe, and that our own subjectivity is completely unrelated to the external world. The ancients Greeks believed in a causation that lay deeper than observable cause-and-effect, what Aristotle called formal causation. In formal causation, a deeper or transcendent principle informs action that on a superficial level is merely observable in terms of cause-and-effect. Hence the material world is the "window dressing" or "wallpapering" of a higher-ordering principle that the ancients knew as the effect of archetypes. We cannot know or see the archetypes or formal causes in-and-of-themselves, however, we can see the effects of these archetypal forces as they inform human behavior and planetary movement.