Aristotle

=== Physics ===
[[File:Four Classical Elements in Burning Log.svg| thumb | The four [[classical element]]s (fire, air, water, earth) of [[Empedocles]] and Aristotle illustrated with a burning log. The log releases all four elements as it is destroyed.]]
{{Main|Aristotelian physics}}

==== Five elements ====
{{Main|Classical element}}

In his ''[[On Generation and Corruption]]'', Aristotle related each of the four elements proposed earlier by [[Empedocles]], [[Earth (classical element)|earth]], [[Water (classical element)|water]], [[Air (classical element)|air]], and [[Fire (classical element)|fire]], to two of the four sensible qualities, hot, cold, wet, and dry. In the Empedoclean scheme, all matter was made of the four elements, in differing proportions. Aristotle's scheme added the heavenly [[Aether (classical element)|aether]], the divine substance of the [[Celestial spheres|heavenly spheres]], stars and planets.{{sfn|Lloyd|1968|pages=133–139, 166–169}}

{| class="wikitable"
|+ [[Classical element|Aristotle's elements]]{{sfn|Lloyd|1968|pages=133–139, 166–169}}
! Element !!{{font color|red|Hot}}/{{font color|blue|Cold}} !!{{font color|green|Wet}}/{{font color|brown|Dry}} !! Motion !! Modern [[State of matter|state<br />of matter]]
|-
|'''[[Earth (classical element)|Earth]]'''||{{font color|blue|Cold}}||{{font color|brown|Dry}}||Down||[[Solid]]
|-
|'''[[Water (classical element)|Water]]'''||{{font color|blue|Cold}}||{{font color|green|Wet}}||Down||[[Liquid]]
|-
|'''[[Air (classical element)|Air]]'''||{{font color|red|Hot}}||{{font color|green|Wet}}||Up||[[Gas]]
|-
|'''[[Fire (classical element)|Fire]]'''||{{font color|red|Hot}}||{{font color|brown|Dry}}||Up||[[Plasma (physics)|Plasma]]
|-
|'''[[Aether (classical element)|Aether]]'''||(divine<br />substance)||—||Circular<br />(in heavens)||[[Vacuum]]
|}

==== Motion ====
{{further | History of classical mechanics}}

Aristotle describes two kinds of motion: "violent" or "unnatural motion", such as that of a thrown stone, in the ''Physics'' (254b10), and "natural motion", such as of a falling object, in ''On the Heavens'' (300a20). In violent motion, as soon as the agent stops causing it, the motion stops also: in other words, the natural state of an object is to be at rest,{{sfn| Allain | 2016}}{{efn-ua | Rhett Allain notes that [[Newton's First Law]] is "essentially a direct reply to Aristotle, that the natural state is ''not to change'' motion.{{sfn| Allain | 2016}}}} since Aristotle does not address [[friction]].{{sfn| Drabkin | 1938 | pp=60–84}} With this understanding, it can be observed that, as Aristotle stated, heavy objects (on the ground, say) require more force to make them move; and objects pushed with greater force move faster.{{sfn| Susskind | 2011}}{{efn-ua | Leonard Susskind comments that Aristotle had clearly never gone [[ice skating]] or he would have seen that it takes force to stop an object.{{sfn| Susskind | 2011}}}} This would imply the equation{{sfn| Susskind | 2011}}

:: <math>F=mv</math>,

incorrect in modern physics.{{sfn| Susskind | 2011}}

Natural motion depends on the element concerned: the aether naturally moves in a circle around the heavens,{{efn-ua | For heavenly bodies like the Sun, Moon, and stars, the observed motions are "to a very good approximation" circular around the Earth's centre, (for example, the apparent rotation of the sky because of the rotation of the Earth, and the rotation of the moon around the Earth) as Aristotle stated.{{sfn| Rovelli | 2015 | pp=23–40}}}} while the 4 Empedoclean elements move vertically up (like fire, as is observed) or down (like earth) towards their natural resting places.{{sfn| Rovelli | 2015 | pp=23–40}}{{sfn| Drabkin | 1938 | pp=60–84}}{{efn-ua | Drabkin quotes numerous passages from ''Physics'' and ''On the Heavens'' (''De Caelo'') which state Aristotle's laws of motion.{{sfn| Drabkin | 1938 | pp=60–84}}}}

[[File:Aristotle's laws of motion.svg| thumb | upright=1.5 | Aristotle's laws of motion. In ''[[Physics (Aristotle)|Physics]]'' he states that objects fall at a speed proportional to their weight and inversely proportional to the density of the fluid they are immersed in.{{sfn| Drabkin | 1938 | pp=60–84}} This is a correct approximation for objects in Earth's gravitational field moving in air or water.{{sfn| Rovelli | 2015 | pp=23–40}}]]

In the ''Physics'' (215a25), Aristotle effectively states a quantitative law, that the speed, v, of a falling body is proportional (say, with constant c) to its weight, W, and inversely proportional to the density,{{efn-ua | Drabkin agrees that density is treated quantitatively in this passage, but without a sharp definition of density as weight per unit volume.{{sfn| Drabkin | 1938 | pp=60–84}}}} ρ, of the fluid in which it is falling:;{{sfn| Rovelli | 2015 | pp=23–40}}{{sfn| Drabkin | 1938 | pp=60–84}}

:: <math>v=c\frac{W}{\rho}</math>

Aristotle implies that in a [[vacuum]] the speed of fall would become infinite, and concludes from this apparent absurdity that a vacuum is not possible.{{sfn| Rovelli | 2015 | pp=23–40}}{{sfn| Drabkin | 1938 | pp=60–84}} Opinions have varied on whether Aristotle intended to state quantitative laws. Henri Carteron held the "extreme view"{{sfn| Drabkin | 1938 | pp=60–84}} that Aristotle's concept of force was basically qualitative,{{sfn| Carteron | 1923 | pages=1–32 and passim}} but other authors reject this.{{sfn| Drabkin | 1938 | pp=60–84}}

[[Archimedes]] corrected Aristotle's theory that bodies move towards their natural resting places; metal boats can float if they [[Archimedes' principle|displace enough water]]; floating depends in Archimedes' scheme on the mass and volume of the object, not, as Aristotle thought, its elementary composition.{{sfn| Rovelli | 2015 | pp=23–40}}

Aristotle's writings on motion remained influential until the [[Early Modern]] period. [[John Philoponus]] (in [[Late antiquity]]) and [[Galileo Galilei|Galileo]] (in [[Early modern period]]) are said to have shown by experiment that Aristotle's claim that a heavier object falls faster than a lighter object is incorrect.{{sfn| Wildberg | 2016}} A contrary opinion is given by [[Carlo Rovelli]], who argues that Aristotle's physics of motion is correct within its domain of validity, that of objects in the [[Earth]]'s gravitational field immersed in a fluid such as air. In this system, heavy bodies in steady fall indeed travel faster than light ones (whether friction is ignored, or not{{sfn| Rovelli | 2015 | pp=23–40}}), and they do fall more slowly in a denser medium.{{sfn| Susskind | 2011}}{{efn-ua | Philoponus and Galileo correctly objected that for the transient phase (still increasing in speed) with heavy objects falling a short distance, the law does not apply: Galileo used balls on a short incline to show this. Rovelli notes that "Two heavy balls with the same shape and different weight do fall at different speeds from an aeroplane, confirming Aristotle's theory, not Galileo's."{{sfn| Rovelli | 2015 | pp=23–40}}}}

Newton's "forced" motion corresponds to Aristotle's "violent" motion with its external agent, but Aristotle's assumption that the agent's effect stops immediately it stops acting (e.g., the ball leaves the thrower's hand) has awkward consequences: he has to suppose that surrounding fluid helps to push the ball along to make it continue to rise even though the hand is no longer acting on it, resulting in the Medieval [[theory of impetus]].{{sfn| Rovelli | 2015 | pp=23–40}}

==== Four causes ====
{{Main|Four causes}}
[[File:Aristotle's Four Causes of a Table.svg| thumb | upright=1.5 | Aristotle argued by analogy with woodwork that a thing takes its form from [[four causes]]: in the case of a table, the wood used ([[material cause]]), its design ([[formal cause]]), the tools and techniques used ([[efficient cause]]), and its decorative or practical purpose ([[final cause]]).{{sfn| Leroi | 2015 | pages=88–90}}]]

Aristotle suggested that the reason for anything coming about can be attributed to four different types of simultaneously active factors. His term ''aitia'' is traditionally translated as "cause", but it does not always refer to temporal sequence; it might be better translated as "explanation", but the traditional rendering will be employed here.{{sfn| Lloyd | 1996 | pages=96–100, 106–107}}{{sfn| Hankinson | 1998 | page=159}}
* [[Material cause]] describes the material out of which something is composed. Thus the material cause of a table is wood. It is not about action. It does not mean that one domino knocks over another domino.{{sfn| Lloyd | 1996 | pages=96–100, 106–107}}
* The [[formal cause]] is its form, i.e., the arrangement of that matter. It tells one what a thing is, that a thing is determined by the definition, form, pattern, essence, whole, synthesis or archetype. It embraces the account of causes in terms of fundamental principles or general laws, as the whole (i.e., macrostructure) is the cause of its parts, a relationship known as the whole-part causation. Plainly put, the formal cause is the idea in the mind of the sculptor that brings the sculpture into being. A simple example of the formal cause is the mental image or idea that allows an artist, architect, or engineer to create a drawing.{{sfn| Lloyd | 1996 | pages=96–100, 106–107}}
* The [[efficient cause]] is "the primary source", or that from which the change under consideration proceeds. It identifies 'what makes of what is made and what causes change of what is changed' and so suggests all sorts of agents, non-living or living, acting as the sources of change or movement or rest. Representing the current understanding of causality as the relation of cause and effect, this covers the modern definitions of "cause" as either the agent or agency or particular events or states of affairs. In the case of two dominoes, when the first is knocked over it causes the second also to fall over.{{sfn| Lloyd | 1996 | pages=96–100, 106–107}} In the case of animals, this agency is a combination of [[developmental biology|how it develops from the egg]], and [[physiology|how its body functions]].{{sfn| Leroi | 2015 | pages=91–92, 369–373}}
* The [[final cause]] (''telos'') is its purpose, the reason why a thing exists or is done, including both purposeful and instrumental actions and activities. The final cause is the purpose or function that something is supposed to serve. This covers modern ideas of motivating causes, such as volition.{{sfn| Lloyd | 1996 | pages=96–100, 106–107}} In the case of living things, it implies [[adaptation]] to a particular way of life.{{sfn| Leroi | 2015 | pages=91–92, 369–373}}

==== Optics ====
{{further | History of optics}}

Aristotle describes experiments in [[optics]] using a [[camera obscura]] in ''[[Problems (Aristotle)|Problems]]'', book 15. The apparatus consisted of a dark chamber with a small [[aperture]] that let light in. With it, he saw that whatever shape he made the hole, the sun's image always remained circular. He also noted that increasing the distance between the aperture and the image surface magnified the image.{{sfn| Lahanas}}

==== Chance and spontaneity ====
{{further | Accident (philosophy)}}

According to Aristotle, spontaneity and chance are causes of some things, distinguishable from other types of cause such as simple necessity. Chance as an incidental cause lies in the realm of [[Accident (philosophy)|accidental things]], "from what is spontaneous". There is also more a specific kind of chance, which Aristotle names "luck", that only applies to people's moral choices.{{sfn| Physics | p=2.6}}{{sfn| Miller | 1973 | pp=204–213}}