Theory of Forms in the context of Platonic philosophy

In semiotics, khôra (also chora; Ancient Greek: χώρα) is the space that gives a place for being. The term has been used in philosophy by Plato to designate a receptacle (as a "third kind" [triton genos]; Timaeus 48e4), a space, a material substratum, or an interval. In Plato's account, khôra is described as a formless interval, alike to a non-being, in between which the "Forms" were received from the intelligible realm (where they were originally held) and were "copied", shaping into the transitory forms of the sensible realm; it "gives space" and has maternal overtones (a womb, matrix):

Platonism is the philosophy of Plato and philosophical systems closely derived from it, though later and contemporary Platonists do not necessarily accept all of Plato's own doctrines. Platonism has had a profound effect on Western thought. At the most fundamental level, Platonism affirms the existence of abstract objects, which are asserted to exist in a third realm distinct from both the sensible external world and from the internal world of consciousness, and is the opposite of nominalism. This can apply to properties, types, propositions, meanings, numbers, sets, truth values, and so on (see abstract object theory). Philosophers who affirm the existence of abstract objects are sometimes called Platonists; those who deny their existence are sometimes called nominalists. The terms "Platonism" and "nominalism" also have established senses in the history of philosophy. They denote positions that have little to do with the modern notion of an abstract object.

In a narrower sense, the term might indicate the doctrine of Platonic realism, a form of mysticism. The central concept of Platonism, a distinction essential to the Theory of Forms, is the distinction between the reality which is perceptible but unintelligible, associated with the flux of Heraclitus and studied by the likes of physical science, and the reality which is imperceptible but intelligible, associated with the unchanging being of Parmenides and studied by the likes of mathematics. Geometry was the main motivation of Plato, and this also shows the influence of Pythagoras. The Forms are typically described in dialogues such as the Phaedo, Symposium and Republic as perfect archetypes of which objects in the everyday world are imperfect copies. Aristotle's Third Man Argument is its most famous criticism in antiquity.

Substance theory, or substance–attribute theory, is an ontological theory positing that objects are constituted each by a substance and properties borne by the substance but distinct from it. In this role, a substance can be referred to as a substratum or a thing-in-itself. Substances are particulars that are ontologically independent: they are able to exist all by themselves. Another defining feature often attributed to substances is their ability to undergo changes. Changes involve something existing before, during and after the change. They can be described in terms of a persisting substance gaining or losing properties. Attributes or properties, on the other hand, are entities that can be exemplified by substances. Properties characterize their bearers; they express what their bearer is like.

Substance is a key concept in ontology, the latter in turn part of metaphysics, which may be classified into monist, dualist, or pluralist varieties according to how many substances or individuals are said to populate, furnish, or exist in the world. According to monistic views, there is only one substance. Stoicism and Spinoza, for example, hold monistic views, that pneuma or God, respectively, is the one substance in the world. These modes of thinking are sometimes associated with the idea of immanence. Dualism sees the world as being composed of two fundamental substances (for example, the Cartesian substance dualism of mind and matter). Pluralist philosophies include Plato's Theory of Forms and Aristotle's hylomorphic categories.

The perennial philosophy (Latin: philosophia perennis), also referred to as perennialism and perennial wisdom, is a school of thought in philosophy and spirituality that posits that the recurrence of common themes across world religions illuminates universal truths about the nature of reality, humanity, ethics, and consciousness. Some perennialists emphasize common themes in religious experiences and mystical traditions across time and cultures; others argue that religious traditions share a single metaphysical truth or origin from which all esoteric and exoteric knowledge and doctrine have developed.

Perennialism has its roots in the Renaissance-era interest in neo-Platonism and its idea of the One from which all existence emerges. Marsilio Ficino (1433–1499) sought to integrate Hermeticism with Greek and Christian thought, discerning a prisca theologia found in all ages. Giovanni Pico della Mirandola (1463–1494) suggested that truth could be found in many—rather than just Biblical and Aristotelian traditions. He proposed a harmony between the thought of Plato and Aristotle and saw aspects of the prisca theologia in Averroes (Ibn Rushd), the Quran, Kabbalah, and other sources. Agostino Steuco (1497–1548) coined the term philosophia perennis.

Aristotle's biology is the theory of biology, grounded in systematic observation and collection of data, mainly zoological, embodied in Aristotle's books on the science. Many of his observations were made during his stay on the island of Lesbos, including especially his descriptions of the marine biology of the Pyrrha lagoon, now the Gulf of Kalloni. His theory is based on his concept of form, which derives from but is markedly unlike Plato's theory of Forms.

The theory describes five major biological processes, namely metabolism, temperature regulation, information processing, embryogenesis, and inheritance. Each was defined in some detail, in some cases sufficient to enable modern biologists to create mathematical models of the mechanisms described. Aristotle's method, too, resembled the style of science used by modern biologists when exploring a new area, with systematic data collection, discovery of patterns, and inference of possible causal explanations from these. He did not perform experiments in the modern sense, but made observations of living animals and carried out dissections. He names some 500 species of bird, mammal, and fish; and he distinguishes dozens of insects and other invertebrates. He describes the internal anatomy of over a hundred animals, and dissected around 35 of these.

Refining is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum will burn straight from the ground, but it will burn poorly and quickly clog an engine with residues and by-products. The term is broad, and may include more drastic transformations, such as the reduction of ore to metal (for which see Refining (metallurgy)).

The refining of liquids is often accomplished by distillation or fractionation; this process is useful, for example, for isolating different fractions of petroleum. Gases can be refined in this way as well, by being cooled and/or compressed until they liquefy. Gases and liquids can also be refined by extraction with a selective solvent that dissolves away either the substance of interest, or the unwanted impurities.

Speusippus (/spjuːˈsɪpəs/; Ancient Greek: Σπεύσιππος; c. 408 – 339/8 BC) was an ancient Greek philosopher. Speusippus was Plato's nephew by his sister Potone. After Plato's death, c. 348 BC, Speusippus inherited the Academy, near age 60, and remained its head for the next eight years. However, following a stroke, he passed the chair to Xenocrates. Although the successor to Plato in the Academy, Speusippus frequently diverged from Plato's teachings. He rejected Plato's Theory of Forms, and whereas Plato had identified the Good with the ultimate principle, Speusippus maintained that the Good was merely secondary. He also argued that it is impossible to have satisfactory knowledge of any thing without knowing all the differences by which it is separated from everything else.

The standard edition of the surviving fragments and testimonies is Leonardo Tarán's Speusippus of Athens: A Critical Study with a Collection of the Related Texts and Commentary (1982).

The Form of the Good or simply the Good, more literally translated as "the Idea of the Good" (Ancient Greek: ἡ τοῦ ἀγαθοῦ ἰδέα), is a concept in the philosophy of Plato. In Plato's Theory of Forms, Forms are abstract ideals that embody the essential qualities of concepts, giving meaning and intelligibility to other objects, such as those in the physical world.

Xenocrates (/zəˈnɒkrəˌtiːz/; Greek: Ξενοκράτης; c. 396/5 – 314/3 BC) of Chalcedon was a Greek philosopher, mathematician, and leader (scholarch) of the Platonic Academy from 339/8 to 314/3 BC. His teachings followed those of Plato, which he attempted to define more closely, often with mathematical elements. He distinguished three forms of being: the sensible, the intelligible, and a third compounded of the two, to which correspond respectively, sense, intellect and opinion. He considered unity and duality to be gods which rule the universe, and the soul a self-moving number. God pervades all things, and there are daemonical powers, intermediate between the divine and the mortal, which consist in conditions of the soul. He held that mathematical objects and the Platonic Ideas are identical, unlike Plato who distinguished them. In ethics, he taught that virtue produces happiness, but external goods can minister to it and enable it to effect its purpose.