Editing Philosophy of science (section)

===Coherentism===
{{main|Coherentism}}
[[File:JeremiahHorrocks.jpg|thumb|[[Jeremiah Horrocks]] makes the first observation of the transit of Venus in 1639, as imagined by the artist [[William Richard Lavender|W.&nbsp;R.&nbsp;Lavender]] in 1903.]]

In contrast to the view that science rests on foundational assumptions, coherentism asserts that statements are justified by being a part of a coherent system. Or, rather, individual statements cannot be validated on their own: only coherent systems can be justified.<ref>{{cite journal|url = http://plato.stanford.edu/archives/spr2014/entries/justep-coherence/|title = Coherentist Theories of Epistemic Justification|access-date = 2015-10-26|last = Olsson|first = Erik|year = 2014|website = Stanford Encyclopedia of Philosophy|editor1-last = Zalta|editor1-first = Edward N.|archive-url = https://web.archive.org/web/20180914115858/https://plato.stanford.edu/archives/spr2014/entries/justep-coherence/|archive-date = 2018-09-14|url-status = live}}</ref> A prediction of a [[transit of Venus]] is justified by its being coherent with broader beliefs about celestial mechanics and earlier observations. As explained above, observation is a cognitive act. That is, it relies on a pre-existing understanding, a systematic set of beliefs. An observation of a transit of Venus requires a huge range of auxiliary beliefs, such as those that describe the [[optics]] of telescopes, the [[mechanics]] of the telescope mount, and an understanding of [[celestial mechanics]]. If the prediction fails and a transit is not observed, that is likely to occasion an adjustment in the system, a change in some auxiliary assumption, rather than a rejection of the theoretical system.{{citation needed|date=December 2017}}

According to the [[Duhem–Quine thesis]], after [[Pierre Duhem]] and [[Willard Van Orman Quine|W.V. Quine]], it is impossible to test a theory in isolation.<ref name="Harding1976">{{cite book|author=Sandra Harding|title=Can theories be refuted?: essays on the Dunhem–Quine thesis|url=https://books.google.com/books?id=Uwit8JTcLfAC&pg=PR9|year=1976|publisher=Springer Science & Business Media|isbn=978-90-277-0630-0|pages=9–|access-date=2016-01-27|archive-url=https://web.archive.org/web/20160628144135/https://books.google.com/books?id=Uwit8JTcLfAC&pg=PR9|archive-date=2016-06-28|url-status=live}}</ref> One must always add auxiliary hypotheses in order to make testable predictions. For example, to test [[Newton's law of universal gravitation|Newton's Law of Gravitation]] in the solar system, one needs information about the masses and positions of the Sun and all the planets. Famously, the failure to predict the orbit of [[Uranus]] in the 19th century led not to the rejection of Newton's Law but rather to the rejection of the hypothesis that the [[Solar System]] comprises only seven planets. The investigations that followed led to the discovery of an eighth planet, [[Neptune]]. If a test fails, something is wrong. But there is a problem in figuring out what that something is: a missing planet, badly calibrated test equipment, an unsuspected curvature of space, or something else.{{citation needed|date=January 2018}}

One consequence of the Duhem–Quine thesis is that one can make any theory compatible with any empirical observation by the addition of a sufficient number of suitable ''ad hoc'' hypotheses. [[Karl Popper]] accepted this thesis, leading him to reject [[Falsifiability#Naive falsificationism|naïve falsification]]. Instead, he favored a "survival of the fittest" view in which the most falsifiable scientific theories are to be preferred.<ref name="Popper 2005ch3-4">{{cite book| last1 = Popper| first1 = Karl| title = The Logic of Scientific Discovery| edition = Taylor & Francis e-Library| year = 2005| publisher = Routledge / Taylor & Francis e-Library| location = London and New York| isbn = 978-0-203-99462-7| at = chapters 3–4}}</ref>