Generally speaking, a god (or "deity") is a being with supernatural powers who receives worship. Not all religions worship a god or gods. There have been an immense number of Gods worshipped throughout history. The Bhakti tradition in Hinduism considers there to be millions of gods.  Many gods are no longer worshipped because their corresponding religion has become extinct. This may also be the fate of currently active religions. Attributes of gods supposedly include:
- perfect or makes mistakes
- being both perfectly just and merciful, which is a contradiction
- impassible and personal, which is a contradiction
- divinely simple
- exists everywhere or is localised
- God is love
- capable of emotions or sometimes not
- have children, either other gods, demi-gods or mortal humans
- the only God, as in monotheism
- one of many Gods, as in polytheism
- identical to reality, as in pantheism
- sovereign, so he can boss people around
- perfect or imperfect
- mortal or immortal
- multi-part but yet unified, as in the Trinity
- self-sufficient, which raises the problem of non-God objects,
- immaterial, just like my invisible pet dragon
- jealous Exodus 34:14
- sometimes incarnated as a human or animal
- omniscient or infallible
- omnibenevolent or capable of evil
- unlike anything else Surah 42:11 Isaiah 40:25
- makes peace and evil Isaiah 45:7
- the best of deceivers Surah 3:54 Surah 8:30
- existence (which is debatable)
There are countless gods, including those of Norse mythology, Greek titans, Greek Olympians, Egyptian mythology, Roman mythology, etc. There are thousands or millions of gods in eastern religions.
Abrahamic god (Yahweh/Jehovah)
- Main Article: Yahweh
In contemporary times, the most popular concept of God is based on the Abrahamic god Yahweh. The original concept of Yahweh has given rise to the Abrahamic religions, including Judaism, Christianity and Islam. While based on a common origin, these religions have significant disagreements about the nature of God.
Christian theology has traditionally defined God (Yahweh) to be the omniscient, omnipotent, and omnibenevolent lone creator of the entire universe. However, some early books of the Bible seem to imply a finite god: In Genesis 18:20-21 , God must personally visit Sodom and Gomorrah to see if they are as wicked as he has been told. In Judges 1:19 , the men of Judah are unable to defeat the people of the plains, in spite of the fact that God was on their side. God's failure in this passage is attributed to the iron chariots of the enemy (this is the basis for the name of IronChariots.org). These is also considerable evidence that Yahweh was one god among many, particularly in early chapters of the Bible.
By far the most straightforward argument against the existence of a god is that there is no evidence for it. An important principle of science is that extraordinary claims require extraordinary evidence.
In the case of the Christian god, we are asked to explain the existence of a vast, complex, incomprehensible universe by inventing an even more vast, complex, incomprehensible being, which also happens to be intelligent enough to "plan" the entire history of the universe and still micromanage the details enough to answer prayers, account for who will go to heaven and hell, and deal with minutiae like how people deal with seemingly arbitrary rules about sex.
Treated purely as an explanatory device, introducing a god into the universe raises far more questions than it answers. It brings up the obvious question of who created God. Science tends to reason from the complex to the simple, finding explanations of natural phenomena by breaking them down into basic rules. Of all the things we know of in the universe, intelligence in particular is one of the most complex and mysterious phenomena observed. To suppose that we could "explain" the universe by introducing a universe-spanning intelligence is completely backwards from the way science normally operates.
All this would be strictly academic nitpicking if there were any positive evidence for the existence of a god. Yet when pressed for evidence, apologists are notoriously vague. Rather than pointing to specific reasons why anyone should believe in such an improbable being, they point to the Bible as a historically accurate text; they bring up philosophical vagaries such as the first cause argument and the argument from design, and they threaten hell by means of Pascal's wager. No test is ever proposed to demonstrate or falsify the existence of God; God's existence is merely assumed to be a default position (which also invokes argumentum ad populum).
"If he is infinitely good, what reason should we have to fear him? If he is infinitely wise, why should we have doubts concerning our future? If he knows all, why warn him of our needs and fatigue him with our prayers? If he is everywhere, why erect temples to him?"
Capitalization of "God"
As a point of grammar, the word "God" is usually capitalized when it refers to a particular god as a proper name; whereas "god" is in lowercase when it refers to one or more of a set of objects. For example: "I do not believe in your god."
Reverential religious texts often take the capitalization a step further when they are talking about their own gods, going so far as to capitalize pronouns that refer to the god. For example: "I love Him"; "We are saved by His grace".
A concept in flux
"The concept of God, even within the same religious tradition, mutates as human societies change. The reaction of nonbelievers changes with it.[...] This flexibility is what keeps the concept of God-of the divine-alive."
- "the idea of God formed in one generation by one set of human beings could be meaningless to another [...There is no fixed concept of God] instead the word contains a whole spectrum of meanings, some of which are contradictory or even mutually exclusive."
- God commanded atrocities in the Old Testament
- God's character changes in the Bible
- God experiences emotions