Why is god, a common noun, capitalized? [duplicate]

When you are referring to the creator of the universe of some religions, you write God; when you are referring to a superhuman being (or a deity) of some other religions, you write god.

The difference is that in monotheistic religions there is only one god, and God often becomes (as in Christianity) a proper noun; in non monotheistic religions (e.g. Hinduism), there isn't a single god, and God is not the name of one of the gods (it is god Vishnu, not God Vishnu).

This is similar to what happen with Moon, used when referring to the natural satellite of planet Earth, and moon, used to refer to the natural satellite of any planet (e.g., Jupiter moons); the same happens with Sun, which is the star around which planet Earth orbits, and sun, which is used to refer any star similar to the Sun (with or without planets).

Answer:

It (and some pronouns), when referring to the creator of the universe, is a proper noun and is capitalized (just like "Bob" or "Joe" would be).

When being used as a common noun, it is referring to the concept of a god (or god as a "type," if you will) and is not capitalized (just like "human" or "dog" would be)

Examples:

The following are all correct:

I pray to God three times a day.

I pray to a god three times a day.

I pray to Him three times a day.

Only religious writings and publications, and material written by the devout, would capitalize pronouns and possessives when in reference to the Christian god. Secular writing is not enjoined to follow the practice. Capitalization of "God" generally serves as a marker for the Judeo-Christian-Islamic deity. Secular writers will usually capitalize "God" out of convention, but not necessarily respect for said deity or the adherents of same.

It depends on whether you subscribe to a monotheistic universe (where you use a capital letter, since there is only one God), or a polytheistic universe (where you use a lower case letter since there are many gods), or an atheistic universe (where you probably use a lower case letter, but don't believe that 'god' exists and avoid the term whenever possible).