theism (thē´Ĭzəm), in theology and philosophy, the belief in a personal God. It is opposed to atheism and agnosticism and is to be distinguished from pantheism and deism (see deists). Unlike pantheists, theists do not hold God to be identical to the universe. Like deists, they believe that God created the universe and transcends it; unlike the deists, they hold that God involves himself in human affairs. For a summary of the arguments that support theism, see God.