Reason

===Subject-centred reason in early modern philosophy===

The [[early modern era]] was marked by a number of significant changes in the understanding of reason, starting in [[Europe]]. One of the most important of these changes involved a change in the [[metaphysics|metaphysical]] understanding of human beings. Scientists and philosophers began to question the teleological understanding of the world.<ref>{{cite web |first=Hubert |last=Dreyfus |title=Telepistemology: Descartes' Last Stand |url=http://socrates.berkeley.edu/~hdreyfus/rtf/Limits_of_Telepresence_6_99.rtf|url-status=dead|archive-url=https://web.archive.org/web/20110521043801/http://socrates.berkeley.edu/~hdreyfus/rtf/Limits_of_Telepresence_6_99.rtf|archive-date=2011-05-21 |publisher= socrates.berkeley.edu |access-date= February 23, 2011}}</ref> Nature was no longer assumed to be human-like, with its own aims or reason, and human nature was no longer assumed to work according to anything other than the same "[[Scientific law|laws of nature]]" which affect inanimate things. This new understanding eventually displaced the previous [[world view]] that derived from a spiritual understanding of the universe.
[[File:Frans Hals - Portret van René Descartes.jpg|thumb|200px|René Descartes]]
Accordingly, in the 17th century, [[René Descartes]] explicitly rejected the traditional notion of humans as "rational animals", suggesting instead that they are nothing more than "thinking things" along the lines of other "things" in nature. Any grounds of knowledge outside that understanding was, therefore, subject to doubt.

In his search for a foundation of all possible knowledge, Descartes decided to throw into doubt ''all'' knowledge—''except'' that of the mind itself in the process of thinking:

<blockquote>At this time I admit nothing that is not necessarily true. I am therefore precisely nothing but a thinking thing; that is a mind, or intellect, or understanding, or reason—words of whose meanings I was previously ignorant.<ref>{{cite book|last=Descartes|first=René|title=[[Meditations on First Philosophy]]|chapter=Concerning the Nature of the Human Mind|year=1641}}</ref></blockquote>

This eventually became known as [[epistemological]] or "subject-centred" reason, because it is based on the ''knowing subject'', who perceives the rest of the world and itself as a set of objects to be studied, and successfully mastered, by applying the knowledge accumulated through such study. Breaking with tradition and with many thinkers after him, Descartes explicitly did not divide the incorporeal soul into parts, such as reason and intellect, describing them instead as one indivisible incorporeal entity.

A contemporary of Descartes, [[Thomas Hobbes]] described reason as a broader version of "addition and subtraction" which is not limited to numbers.<ref>{{Citation|chapter=Of Philosophy|title=Elements of Philosophy I: De Corpore|url=https://archive.org/details/englishworkstho21hobbgoog|last=Hobbes|first=Thomas|editor-first=William|editor-last=Molesworth|location=London|publisher=J. Bohn|year=1839|orig-year=1655|page=5|quote=We must not therefore think that computation, that is, ratiocination, has place only in numbers, as if man were distinguished from other living creatures (which is said to have been the opinion of ''[[Pythagoras]]'') by nothing but the faculty of numbering; for ''magnitude, body, motion, time, degrees of quality, action, conception, proportion, speech and names'' (in which all the kinds of philosophy consist) are capable of addition and substraction {{sic}}. Now such things as we add or substract, that is, which we put into an account, we are said to ''consider'', in Greek {{lang|grc|λογίζεσθαι}} [{{transliteration|grc|logizesthai}}], in which language also {{lang|grc|συλλογίζεσθι}} [{{transliteration|grc|syllogizesthai}}] signifies to ''compute'', ''reason'', or ''reckon''.}}</ref> This understanding of reason is sometimes termed "calculative" reason. Similar to Descartes, Hobbes asserted that "No discourse whatsoever, can end in absolute knowledge of fact, past, or to come" but that "sense and memory" is absolute knowledge.<ref>{{multiref2
|1={{citation|first=Thomas|last=Hobbes|title=Leviathan|chapter=Of the ends, or resolutions of discourse|chapter-url=https://archive.org/details/in.ernet.dli.2015.224021/page/n65/mode/2up|year=1651}}
|2={{citation|first=Thomas|last=Hobbes|title=Leviathan|chapter=Of the several subjects of knowledge|chapter-url=https://archive.org/details/in.ernet.dli.2015.224021/page/n76/mode/1up|year=1651}}
}}</ref>

In the late 17th century through the 18th century, [[John Locke]] and [[David Hume]] developed Descartes's line of thought still further. Hume took it in an especially [[skepticism|skeptical]] direction, proposing that there could be no possibility of [[deductive reasoning|deducing]] relationships of cause and effect, and therefore no knowledge is based on reasoning alone, even if it seems otherwise.<ref>{{multiref2
|1={{cite book|first=John|last=Locke|chapter=Of Identity and Diversity|year=1689|chapter-url=https://archive.org/details/in.ernet.dli.2015.223061/page/n257/mode/2up|title=An Essay concerning Human Understanding|volume=II}}
|2={{cite book|first=David |last=Hume|chapter=Of Personal Identity|chapter-url=https://archive.org/details/0213-bk/page/251/mode/1up|title=A Treatise of Human Nature|volume=I.4|year=1740}}
}}</ref>

Hume famously remarked that, "We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them."<ref>{{citation|first=David |last=Hume|chapter=Of the influencing motives of the will|chapter-url=https://archive.org/details/0213-bk/page/413/mode/1up|title=A Treatise of Human Nature|volume=II.3|year=1740}}</ref> Hume also took his definition of reason to unorthodox extremes by arguing, unlike his predecessors, that human reason is not qualitatively different from either simply conceiving individual ideas, or from judgments associating two ideas,<ref>{{citation|first=David |last=Hume|chapter=Of the Nature of the Idea Or Belief|chapter-url=https://archive.org/details/0213-bk/page/94/mode/1up8|title=A Treatise of Human Nature|volume=I.3|year=1740|at=[https://archive.org/details/0213-bk/page/96/mode/1up footnote 1]}}</ref> and that "reason is nothing but a wonderful and unintelligible instinct in our souls, which carries us along a certain train of ideas, and endows them with particular qualities, according to their particular situations and relations."<ref name=HumeI3xvi>{{citation|first=David |last=Hume|chapter=Of the reason of animals|chapter-url=https://archive.org/details/0213-bk/page/176/mode/2up|title=A Treatise of Human Nature|volume=I.3|year=1740}}</ref> It followed from this that animals have reason, only much less complex than human reason.

In the 18th century, [[Immanuel Kant]] attempted to show that Hume was wrong by demonstrating that a "[[transcendental arguments|transcendental]]" self, or "I", was a necessary condition of all experience. Therefore, suggested Kant, on the basis of such a self, it is in fact possible to reason both about the conditions and limits of human knowledge. And so long as these limits are respected, reason can be the vehicle of morality, justice, aesthetics, theories of knowledge ([[epistemology]]), and understanding.{{cn|reason=|date=September 2023}}