Editing Raven paradox (section)

== Paradox ==

Hempel describes the paradox in terms of the [[hypothesis]]:<ref name="JSTOR">{{cite journal |last=Hempel |first=C. G. |year=1945 |title=Studies in the Logic of Confirmation I |journal=[[Mind (journal)|Mind]] |volume=54 |issue=13 |pages=1–26 |url=http://www.philoscience.unibe.ch/documents/TexteHS10/Hempel1945.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.philoscience.unibe.ch/documents/TexteHS10/Hempel1945.pdf |archive-date=2022-10-09 |url-status=live |jstor=2250886 |doi=10.1093/mind/LIV.213.1 }}</ref><ref>{{cite journal |last=Hempel |first=C. G. |year=1945 |title=Studies in the Logic of Confirmation II |journal=[[Mind (journal)|Mind]] |volume=54 |issue=214 |pages=97–121 |url=http://www.collier.sts.vt.edu/5305/hempel-II.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.collier.sts.vt.edu/5305/hempel-II.pdf |archive-date=2022-10-09 |url-status=live | jstor=2250948 |doi=10.1093/mind/LIV.214.97 }}</ref>
: (1) ''All [[raven]]s are black''. In the form of an implication, this can be expressed as: ''If something is a raven, then it is black.''

Via [[contraposition]], this statement is [[Logical equivalence|equivalent]] to:
: (2) ''If something is not black, then it is not a raven.''

In all circumstances where (2) is true, (1) is also true—and likewise, in all circumstances where (2) is false (i.e., if a world is imagined in which something that was not black yet was a raven existed), (1) is also false.

Given a general statement such as ''all ravens are black'', a form of the same statement that refers to a specific observable instance of the general class would typically be considered to constitute evidence for that general statement. For example,
: (3) ''My pet raven is black.''
is evidence supporting the hypothesis that ''all ravens are black''.

The paradox arises when this same process is applied to statement (2). On sighting a green apple, one can observe:
: (4) ''This green apple is not black, and it is not a raven.''
By the same reasoning, this statement is evidence that (2) ''if something is not black then it is not a raven.'' But since (as above) this statement is logically equivalent to (1) ''all ravens are black'', it follows that the sight of a green apple is evidence supporting the notion that all ravens are black. This conclusion seems paradoxical because it implies that information has been gained about ravens by looking at an apple.