Which of the following best defines metaphysics?

The definition of metaphysics aligns closely with the exploration of fundamental questions about the nature of reality and existence. Metaphysics delves into concepts such as what it means to exist, the nature of objects and their properties, and the relationships and principles governing the universe. It goes beyond physical science to consider the underlying nature of reality itself, including abstract concepts like being, reality, cause and effect, and the nature of objects.

Contrastingly, other options refer to different fields of study: the study of human behavior is related to psychology and sociology, the study of knowledge and belief pertains to epistemology, and the study of principles of beauty is associated with aesthetics. Each of these areas addresses specific aspects of experience but does not encompass the broader inquiries of existence and reality that define metaphysics. Thus, the focus on nature and existence makes the chosen answer the most accurate representation of metaphysics.