Illusion in the context of "Optical illusion"

Henry David Thoreau (born David Henry Thoreau; July 12, 1817 – May 6, 1862) was an American naturalist, essayist, poet, and philosopher. A leading transcendentalist, he is best known for his book Walden, a reflection upon simple living in natural surroundings, and his essay "Civil Disobedience" (originally published as "Resistance to Civil Government"), an argument in favor of citizen disobedience against an unjust state.

Thoreau's books, articles, essays, journals, and poetry amount to more than 20 volumes. Among his lasting contributions are his writings on natural history and philosophy, in which he anticipated the methods and findings of ecology and environmental history, two sources of modern-day environmentalism. His literary style interweaves close observation of nature, personal experience, pointed rhetoric, symbolic meanings, and historical lore, while displaying a poetic sensibility, philosophical austerity, and attention to practical detail. He was also deeply interested in the idea of survival in the face of hostile elements, historical change, and natural decay; at the same time he advocated abandoning waste and illusion in order to discover life's true essential needs.

Philosophical realism—usually not treated as a position of its own but as a stance towards other subject matters—is the view that a certain kind of thing (ranging widely from abstract objects like numbers to moral statements to the physical world itself) has mind-independent existence, i.e. that it exists even in the absence of any mind perceiving it or that its existence is not just a mere appearance in the eye of the beholder. This includes a number of positions within epistemology and metaphysics which express that a given thing instead exists independently of knowledge, thought, or understanding. This can apply to items such as the physical world, the past and future, other minds, and the self, though may also apply less directly to things such as universals, mathematical truths, moral truths, and thought itself. However, realism may also include various positions which instead reject metaphysical treatments of reality altogether.

Realism can also be a view about the properties of reality in general, holding that reality exists independent of the mind, as opposed to non-realist views (like some forms of skepticism and solipsism) which question the certainty of anything beyond one's own mind. Philosophers who profess realism often claim that truth consists in a correspondence between cognitive representations and reality.

Magic is a performing art in which audiences are entertained by tricks, effects, or illusions of seemingly impossible feats, using natural means. It encompasses the subgenres of close-up magic, parlor magic, and stage magic, among others. It is to be distinguished from paranormal magic which are effects claimed to be created through supernatural means. It is one of the oldest performing arts in the world.

Modern entertainment magic, as pioneered by 19th-century magician Jean-Eugène Robert-Houdin, has become a popular theatrical art form. In the late 19th and early 20th centuries, magicians such as John Nevil Maskelyne and David Devant, Howard Thurston, Harry Kellar, and Harry Houdini achieved widespread commercial success during what has become known as "the Golden Age of Magic", a period in which performance magic became a staple of Broadway theatre, vaudeville, and music halls. Meanwhile, magicians such as Georges Méliès, Gaston Velle, Walter R. Booth, and Orson Welles introduced pioneering filmmaking techniques informed by their knowledge of magic.

Gnosticism (from Ancient Greek γνωστικός (gnōstikós) 'having knowledge'; Koine Greek: [ɣnostiˈkos]) is a collection of religious and philosophical ideas and systems that coalesced in the late first century AD among sects of early Christianity and other faiths. It is not a singular, homogeneous tradition or religion, but an umbrella term used by modern scholars to describe different groups and beliefs that shared certain characteristics. These diverse Gnostic groups generally emphasized personal spiritual knowledge (gnosis) above the authority, traditions, and proto-orthodox teachings of organized religious institutions. The Gnostic worldview typically distinguished between a hidden, uncorrupted supreme being and a flawed demiurge responsible for creating material reality. Gnostics held this material existence to be evil and believed the principal element of salvation was direct knowledge of the supreme divinity, attained via mystical or esoteric insight. Many Gnostic texts deal not in concepts of sin and repentance, but with illusion and enlightenment.

Although the exact origins of Gnosticism cannot be traced, Gnostic writings flourished among certain Christian groups in the Mediterranean during the second century. In the Gnostic Christian tradition, Christ was seen as a divine being that had taken human form in order to lead humanity back to recognition of its own divine nature. Judean–Israelite Gnosticism, including the Mandaeans and Elkesaites, blended Jewish-Christian ideas with Gnostic beliefs focused on baptism and the cosmic struggle between light and darkness. Syriac–Egyptian groups like Sethianism and Valentinianism combined Platonic philosophy and Christian themes, seeing the material world as flawed but not wholly evil. Other traditions include the Basilideans, Marcionites, and Thomasines. Manichaeism, which adopted Gnostic concepts such as cosmic dualism, emerged as a major religious movement in the third century, briefly rivaling Christianity.

Subjective idealism, or empirical idealism or immaterialism, is a form of philosophical monism that holds that only minds and mental contents exist. It entails and is generally identified or associated with immaterialism, the doctrine that material things do not exist. Subjective idealism rejects dualism, neutral monism, and materialism; it is the contrary of eliminative materialism, the doctrine that all or some classes of mental phenomena (such as emotions, beliefs, or desires) do not exist, but are sheer illusions.

Levitation or transvection, in the paranormal or religious context, is the claimed ability to raise a human body or other object into the air by mystical means.

While believed in some religious and New Age communities to occur due to supernatural, miraculous, psychic, or "energetic" phenomena, there is no scientific evidence of levitation occurring. Alleged cases of levitation can usually be explained by deception and fraud, such as trickery, illusion, and hallucination.

A hallucination is a perception in the absence of an external context stimulus that has the compelling sense of reality. They are distinguishable from several related phenomena, such as dreaming (REM sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional significance.

Hallucinations can occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. Hallucinations are referred to as multimodal if multiple sensory modalities occur.