Final answer:
The two possible approaches to existence and naturalistic assumptions are materialism, which believes only in physical substance, and dualism, which posits both material and immaterial aspects to existence. These fall within the broader field of metaphysics, which studies the fundamental nature of reality.
Step-by-step explanation:
The debate over the approaches to existence and the naturalistic assumptions about existence and man can be broadly classified into philosophical positions like materialism, idealism, dualism, and existentialism. The two possible approaches to existence and naturalistic assumptions about existence and man, as given by the options, are materialism and dualism.
Materialism posits that only material or physical substance exists, and there is no spiritual or immaterial aspect to existence. On the contrary, dualism is the view that posits two types of being—material and immaterial (or spiritual)—to account fully for the nature of existence, including both the physical and the mental aspects of the human condition.
On a broader scale, these perspectives are part of metaphysical inquiry, which is the field of philosophy that pursues the fundamental nature of reality, considering concepts like substance, identity, and the nature of consciousness. While materialism aligns with naturalism's rejection of the supernatural, dualism allows room for a non-physical realm or dimension to coexist alongside the physical universe.