Editing Unobservable (section)

== Kinds of unobservables ==
W. V. Metcalf distinguishes three kinds of unobservables.<ref>{{cite journal |last=Metcalf |first=W. V. |date=1940 |title=The Reality of the Unobservable |jstor=184849 |journal=Philosophy of Science |volume=7 |issue=3 |pages=337–341 |doi=10.1086/286640|s2cid=121713405 }}</ref> One is the logically unobservable, which involves a contradiction. An example would be a length which is both longer and shorter than a given length. The second is the practically unobservable, that which we can conceive of as observable by the known sense-faculties of man but we are prevented from observing by practical difficulties. The third kind is the physically unobservable, that which can never be observed by any existing sense-faculties of man.