Deities and ghosts are simply spirits. Since the subject of spirits is not within the realm of science, it is looked upon as superstition by a lot of people. Some people who claim to be experts in metaphysics also do not like to talk about spirits. We must understand that metaphysics is the rational study of our universe beyond the coverage of physics. Spirits are what science cannot cover. If spirits do not exist, then there is practically nothing left in metaphysics.
The following short paragraph is from Xi Ci Zhuan 繫辭傳 of the Yijing 易經.
仰以觀於天文 俯以察於地理 是故知幽明之故
精氣為物 游魂為變 是故知鬼神之情狀
"The Yi is based on the principle of Heaven and Earth. Therefore, it can explain the way of Heaven and Earth. (The sages) look up to examine astronomy, look down to study geography. They therefore understand the reasons for brightness and darkness. They explore the beginning and the ending and therefore understand the theory of life and death. Essence and breath form tangible beings. The wandering of spirits causes the transformation. Therefore, they know the situation of deities and ghosts." - translation by Joseph Yu
The Yijing is the origin of Chinese metaphysics. It clearly points out the structure of living things - formation of the body by assimilation of essence and breath with life and death controlled by the movement of spirit.
The combination of a body and a spirit brings life. The departure of the spirit from the body implies death.
Spirits are therefore quite close to us and are nothing to be afraid of. They are the core of the study of Destiny and Feng Shui. Metaphysics can therefore be defined as the rational analysis of irrational beings to see how they affect the lives of people.