Theism is broadly defined as the belief in the existence of a Supreme Being or deities. In common parlance, or when contrasted with deism, the term often describes the classical conception of God that is found in monotheism – or gods found in polytheistic religions—a belief in God or in gods without the rejection of revelation as is characteristic of deism. Atheism is commonly understood as rejection of theism in the broadest sense of theism, i.e. the rejection of belief in God or gods. The claim that the existence of any deity is unknown or unknowable is agnosticism.
Etymology
The term theism derives from the Greektheos or theoi meaning "god" or "gods". The term theism was first used by Ralph Cudworth. In Cudworth's definition, they are "strictly and properly called Theists, who affirm, that a perfectly conscious understanding being, or mind, existing of itself from eternity, was the cause of all other things".
Polytheism is the belief that there is more than one god. In practice, polytheism is not just the belief that there are multiple gods; it usually includes belief in the existence of a specific pantheon of distinct deities. Within polytheism there are hard and soft varieties:
Soft polytheism views the gods as being subsumed into a greater whole. Some other forms of Hinduism such as Smartism/Advaita Vedanta serve as examples of soft polytheism.
Polytheism is also divided according to how the individual deities are regarded:
Henotheism: The viewpoint/belief that there may be more than one deity, but only one of them is worshiped.
Kathenotheism: The viewpoint/belief that there is more than one deity, but only one deity is worshiped at a time or ever, and another may be worthy of worship at another time or place. If they are worshiped one at a time, then each is supreme in turn.
Monolatrism: The belief that there may be more than one deity, but that only one is worthy of being worshiped. Most of the modern monotheistic religions may have begun as monolatric ones, although this is disputed.
Pantheism: The belief that the physical universe is equivalent to god, and that there is no division between a Creator and the substance of its creation.
Panentheism: Like Pantheism, the belief that the physical universe is joined to a god or gods. However, it also believes that the divine pervades and interpenetrates every part of the universe and also extends beyond time and space. Examples include most forms of Vaishnavism and the philosophy of Baruch Spinoza.
The distinction between these two beliefs may be ambiguous and unhelpful, or a significant point of division. Pantheism may be understood a type of Nontheism, where the physical universe takes on some of the roles of a theistic God, and other roles of God viewed as unnecessary.
Deism
Classical Deism is the belief that one God exists and created the world, but that the Creator does/do not alter the original plan for the universe, but presides over it in the form of Providence; however, some classical Deists did believe indivine intervention.
Autotheism is the viewpoint that divinity, whether also external or not, is inherently within 'oneself' and that one has the ability to become godlike. This can be in a selfless way, a way following the implications of statements attributed to ethical, philosophical, and religious leaders. Autotheism can also refer to the belief that one's self is a deity, within the context of subjectivism. Hindus use the term, "aham Brahmāsmi" which means, "I am Brahman".
Value-judgment theisms
Eutheism is the belief that a deity is wholly benevolent.
Dystheism is the belief that a deity is not wholly good, and is possibly evil.
Maltheism is the belief that a deity exists, but is wholly malicious.
