In Western civilization, Idealism is the philosophy which maintains that the ultimate nature of reality is based upon ideas, values and essences and that the external, or real world is inseparable from consciousness, perception, mind, intellect and reason in the sense of rigorous science.

In certain idealistic philosophies the ideal is said to involve direct and immediate knowledge of subjective mental ideas, or images. Idealism is often opposed to realism in which the real is said to have an absolute existence prior to, and independent of, knowledge and consciousness. Epistemological idealists such as Immanuel Kant might insist that the only things which can be directly known for certain are ideas.

Some forms of idealism, like that of Rene Descartes, are often contrasted with materialism. Some idealists, like Baruch Spinoza, are monist as opposed to dualist.

A broad enough definition of idealism could include most religious viewpoints. The belief that personal beings such as Gods, angels and spirits preceded the existence of insentient matter seems to suggest that an experiencing subject is a necessary reality. Also, the existence of an omniscient God suggests, regardless of the actual nature of matter, that all of nature is the object of at least one consciousness.

Materialism sees no incoherence in a scenario of there being a cosmos where no sentient subject ever develops. A wholly unknown universe where neither any subject, nor any object of a subject’s experience ever exists. Historically, Mechanistic Materialism has been the favorite viewpoint of Atheist philosophers. Still, idealistic viewpoints that have not included God, supernatural beings, or a post-mortem existence have sometimes been advanced.

Many religious philosophies are indeed specifically idealist. Some Hindu denominations view regarding the nature of Brahman, souls, and the world as idealistic, and some have favored a form of substance dualism. Early Buddhism was not subjective idealistic. Some have misinterpreted the Yogācāra school of Mahayana Buddhism that developed the consciousness only approach as a form of metaphysical idealism, but this is incorrect. Yogācāra thinkers did not focus on consciousness to assert it as ultimately real. Yogācāra claims consciousness is only conventionally real since it arises from moment to moment due to fluctuating causes and conditions.

Some Christian theologians have held idealist views. Substance dualism has been the more common view of Christian authors, especially with the strong influence of the philosophy of Aristotle among the Scholastics. 

Several modern religious movements, for example the organizations within the New Thought Movement and the Unity Church, may be said to have a particularly idealist orientation.

The theology of Christian Science includes a form of subjective idealism: it teaches that all that exists is God and God’s ideas; that the world as it appears to the senses is a distortion of the underlying spiritual reality.

A Course in Miracles, a spiritual self study course published in 1976, represents an explicitly idealist, pure nondualistic thought system. In the course, only God and His Creation, which is Spirit and has nothing to do with the world, are real. The physical universe is an illusion and does not exist. The Course compares the world of perception with a dream. It arises from the projection of the dreamer. The purpose of the perceptual world is to ensure our separate, individual existence apart from God but avoid the responsibility and project the blame onto others. As we learn to give the world another purpose and recognize our perceptual errors, we also learn to look past them as a way to awaken gradually from the dream and finally remember our true Identity in God. The Course’s nondualistic metaphysics is similar to the Advaita Vedanta school of Hindu philosophy.

Theologians and philosophers have ascribed a number of attributes to God, including omniscience, omnipotence, omnipresence, perfect goodness, divine simplicity, and eternal and necessary existence. God has been described as incorporeal, a personal being, the source of all moral obligation, and the greatest conceivable being existent. These attributes were all claimed to varying degrees by the early Jewish, Christian and Muslim scholars.

Many medieval philosophers developed arguments for the existence of God, while attempting to comprehend the precise implications of God’s attributes. Reconciling some of those attributes generated important philosophical problems and debates. For example, God’s omniscience implies that God knows how free agents will choose to act. If God does know this, their apparent free will might be illusory, or foreknowledge does not imply predestination, and if God does not know it, God is not omniscient.

The last centuries of philosophy have seen vigorous questions regarding the arguments for God’s existence raised by such philosophers as Immanuel Kant, David Hume and Antony Flew, although Kant held that the argument from morality was valid. The theist response has been either to contend, like Alvin Plantinga, that faith is properly basic, or to take, like Richard Swinburne, the evidentialist position. Some theists agree that none of the arguments for God’s existence are compelling, but argue that faith is not a product of reason, but requires risk. There would be no risk, they say, if the arguments for God’s existence were as solid as the laws of logic, a position summed up by Pascal as “The heart has reasons which reason knows not of.”

Most major religions hold God not as a metaphor, but a being that influences our day-to-day existences. Many believers allow for the existence of other, less powerful spiritual beings, and give them names such as angels, saints, djinni, demons, and devas.

Through the present moment we have access to the power of life itself, that which has traditionally been called God. As soon as we turn away form it, God ceases to be a reality in our lives, and all we are left with is the mental concept of God, which some people believe in and others deny. Even belief in God is only a poor substitute for the living reality of God manifesting every moment of our lives.

Our minds reveal themselves as essentially formless when we go deeper into them. They become a doorway into inner space. Although inner space has no form, it is intensely alive. That empty space is life in its fullness, the unmanifested source out of which all manifestation flows. The traditional word for that source is God.

So when we think we can sense our thoughts, that is a misperception created by our minds. What is really happening is that the consciousness that appears as the mind is becoming conscious of itself. When we no longer confuse who we are with a temporary form of ourselves, then the dimension of the limitless and the eternal can express itself through us and guide us. At each moment, we can sense the presence of inner space, which really means we can sense our own presence within the presence of God.