Introduction: Two-Way Powers: Historical and Contemporary Perspectives

Powers pervade the natural world, from a flame’s power to burn to a plant’s power to grow. Certain powers seem to be special in being two-way . A two-way power is a single, unified power to do something or its opposite. Whereas a plant’s circumstances determine that it will grow, I seem to have the power to raise my arm or refrain from doing so: it is up to me whether or not to raise it. If this is right, then this power of mine is a two-way power.