Editing Extension (metaphysics) (section)

==History==
===Descartes===
[[René Descartes]] defined extension as the property of existing in more than one dimension, a property that was later followed up in [[Grassmann algebra|Grassmann's n-dimensional algebra]]. For Descartes, the primary characteristic of [[matter]] is extension (''res extensa''), just as the primary characteristic of [[mind]] is [[thought]] (''res cogitans'').

===Newton===
After rejecting Cartesian identification of body with extension, [[Isaac Newton|Newton]] turns to the question of what the nature of the "immobile being"&mdash;space or extension itself, distinguished from body&mdash;was. He raises three possible definitions for extension: as a kind of ''substance''; or as a kind of ''accident'' (a standard philosophical term for ''attribute'': anything that can be predicated of substance); or "''simply nothing''" (a reference to atomism), all of which he repudiates. Instead he proposes that extension "has a certain mode of existence of its own, which agrees neither with substances nor accidents."<ref name=Stein>{{cite book|author-last=Stein|author-first=Howard|year=2016|title=Newton's metaphysics: The Cambridge Companion to Newton|page=333|doi=10.1017/cco9781139058568.010|publisher=[[Cambridge University Press]]|quote=as for instance is plain from this, that they would easily concede extension to be a substance like a body if only it could move and could exercise the actions of a body; and on the other hand, they would by no means concede a body to be a substance if it neither could move nor arouse any sensation or perception in any mind whatever.}}</ref> After struggling with this question, Newton provides perhaps one of the clearest definitions of extension

{{quote|''If we say with Descartes that extension is body, do we not manifestly offer a path to Atheism, both because extension is not a creature but has existed eternally, and because we have an absolute Idea of it without any relationship to God, and therefore we are able to conceive of it as existent while feigning the non-existence of God?''<ref name=Stein/>}}

which lead Stein to conclude Newton's conception of Space, the existence of space, or extension, ''follows from'' that of anything whatsoever; but extension does not require a subject in which it "inheres", as a property; and it can be conceived as existent without presupposing any ''particular'' thing, God included. On the other hand, it is an "affection of every being."<ref name=Stein/>

===Locke===
[[John Locke]], in ''[[An Essay Concerning Human Understanding]]'', defined extension as "only the Space that lies between the Extremities of those solid coherent Parts" of a body.<ref>{{cite book |title=An Essay Concerning Human Understanding, Volume 1 |last=Locke |first=John |authorlink=John Locke |year=1816 |publisher=B. Smith|page= 131|url=https://books.google.com/books?id=r9sUAAAAQAAJ&dq=%22only+the+space+that+lies+between+the+extremities+of+the+solid+coherent+parts%22&pg=PA131}}</ref>  It is the space possessed by a body. Locke refers to the extension in conjunction with ''[[solidity]]'' and ''[[impenetrability]],'' the other primary characteristics of matter.<ref>{{cite book |title=An Essay Concerning Human Understanding, Volume 1 |last=Locke |first=John |authorlink=John Locke |year=1816 |publisher=B. Smith|pages= 131–132|url=https://books.google.com/books?id=r9sUAAAAQAAJ&dq=%22only+the+space+that+lies+between+the+extremities+of+the+solid+coherent+parts%22&pg=PA131}}</ref>

===Spinoza===
Extension also plays an important part in the philosophy of [[Baruch Spinoza]], who says that substance (that which has extension) can be limited only by substance of the same sort, i.e. matter cannot be limited by ideas and vice versa. From this principle, he determines that substance is infinite. This infinite substance is what Spinoza calls [[God]], or better yet [[nature]], and it possesses both unlimited extension and unlimited consciousness.