Aristotle

==== Substance ====
{{further | Hylomorphism }}

Aristotle examines the concepts of [[Substance theory|substance]] (''ousia'') and [[essence]] (''to ti ên einai'', "the what it was to be") in his ''Metaphysics'' (Book VII), and he concludes that a particular substance is a combination of both matter and form, a philosophical theory called [[hylomorphism]]. In Book VIII, he distinguishes the matter of the substance as the [[Material substratum|substratum]], or the stuff of which it is composed. For example, the matter of a house is the bricks, stones, timbers, etc., or whatever constitutes the ''potential'' house, while the form of the substance is the ''actual'' house, namely 'covering for bodies and chattels' or any other [[Genus-differentia definition|differentia]] that let us define something as a house. The formula that gives the components is the account of the matter, and the formula that gives the differentia is the account of the form.{{sfn| Metaphysics | p=VIII 1043a 10–30}}{{sfn| Cohen | 2000}}

===== Immanent realism =====
{{Main|Aristotle's theory of universals}}
[[File:Platonic and Aristotelian Forms.svg| thumb | upright=1.5 | [[Plato]]'s [[Theory of forms|forms]] exist as [[universals]], like the ideal form of an apple. For Aristotle, both matter and form belong to the individual thing ([[hylomorphism]]).]]
Like his teacher Plato, Aristotle's philosophy aims at the [[Problem of universals|universal]]. Aristotle's [[ontology]] places the universal (''katholou'') in [[particular]]s (''kath' hekaston''), things in the world, whereas for Plato the universal is a separately existing form which actual things imitate. For Aristotle, "form" is still what [[phenomena]] are based on, but is "instantiated" in a particular substance.{{sfn| Cohen | 2000}}

Plato argued that all things have a [[Theory of forms|universal form]], which could be either a property or a relation to other things. When one looks at an apple, for example, one sees an apple, and one can also analyse a form of an apple. In this distinction, there is a particular apple and a universal form of an apple. Moreover, one can place an apple next to a book, so that one can speak of both the book and apple as being next to each other. Plato argued that there are some universal forms that are not a part of particular things. For example, it is possible that there is no particular good in existence, but "good" is still a proper universal form. Aristotle disagreed with Plato on this point, arguing that all universals are instantiated at some period of time, and that there are no universals that are unattached to existing things. In addition, Aristotle disagreed with Plato about the location of universals. Where Plato spoke of the forms as existing separately from the things that participate in them, Aristotle maintained that universals exist within each thing on which each universal is predicated. So, according to Aristotle, the form of apple exists within each apple, rather than in the world of the forms.{{sfn| Cohen | 2000}}{{sfn|Lloyd|1968|pages=43–47}}

===== Potentiality and actuality =====
Concerning the nature of change (''[[Potentiality and actuality|kinesis]]'') and its causes, as he outlines in his ''[[Physics (Aristotle)|Physics]]'' and ''[[On Generation and Corruption]] (''319b–320a), he distinguishes coming-to-be (''genesis'', also translated as 'generation') from:

# growth and diminution, which is change in quantity;
# locomotion, which is change in space; and
# alteration, which is change in quality.

[[File:Flute-player dolphin Alcesti Group MAN.jpg| thumb | Aristotle argued that a capability like playing the flute could be acquired – [[Potentiality and actuality (Aristotle)|the potential made actual]] – by learning.]]

Coming-to-be is a change where the substrate of the thing that has undergone the change has itself changed. In that particular change he introduces the concept of potentiality (''[[Dunamis|dynamis]]'') and actuality (''[[entelecheia]]'') in association with the matter and the form. Referring to potentiality, this is what a thing is capable of doing or being acted upon if the conditions are right and it is not prevented by something else. For example, the seed of a plant in the soil is potentially (''dynamei'') a plant, and if it is not prevented by something, it will become a plant. Potentially, beings can either 'act' (''poiein'') or 'be acted upon' (''paschein''), which can be either innate or learned. For example, the eyes possess the potentiality of sight (innate – being acted upon), while the capability of playing the flute can be possessed by learning (exercise – acting). Actuality is the fulfilment of the end of the potentiality. Because the end (''telos'') is the principle of every change, and potentiality exists for the sake of the end, actuality, accordingly, is the end. Referring then to the previous example, it can be said that an actuality is when a plant does one of the activities that plants do.{{sfn| Cohen | 2000}}

{{blockquote | For that for the sake of which (''to hou heneka'') a thing is, is its principle, and the becoming is for the sake of the end; and the actuality is the end, and it is for the sake of this that the potentiality is acquired. For animals do not see in order that they may have sight, but they have sight that they may see.{{sfn| Metaphysics | p=IX 1050a 5–10}}}}

In summary, the matter used to make a house has potentiality to be a house and both the activity of building and the form of the final house are actualities, which is also a [[final cause]] or end. Then Aristotle proceeds and concludes that the actuality is prior to potentiality in formula, in time and in substantiality. With this definition of the particular substance (i.e., matter and form), Aristotle tries to solve the problem of the unity of the beings, for example, "what is it that makes a man one"? Since, according to [[Plato]] there are two Ideas: animal and biped, how then is man a unity? However, according to Aristotle, the potential being (matter) and the actual one (form) are one and the same.{{sfn| Cohen | 2000}}{{sfn| Metaphysics | p=VIII 1045a–b}}