Among philosophers, circularity is a rather popular issue. Given this, it is an amazing fact that the understanding of circularity (among philosophers; but then only philosophers are interested in circularity at all anyway) is rather moderate.
In particular, it is sometimes neglected that there are quite a number of different types of circularity. (Indeed, many philosophers, including some rather prominent ones, seem to be just unawares of the fact, even though at least the first two of these types--circularity of arguments and circularity of definitions--are both commonly represented within introductory logic books) .
Here are four types of circularity (the list may be inexhaustive):
(1) circularity of argument (highly problematic)
o [*] circular explanation of an argument / of reasons for thinking ...
KEYWORDS: 'question-begging' / begging the question (goes back to Aristotle); petitio principii.
EXAMPLE: Schlick, Carnap (among others) use the assumption that meaning consists in conditions/methods of verification in the course of arguing for the view that statements which are not empirically verifiable (falsifiable) are meaningless.
REMARK: Usually occurs in connection with definitions (or re-definitions) of (technical) terms.
(2) circularity of definition (often not too problematic)
o [*] circular explanation of the meaning of a term.
EXAMPLE: In Searle & Vanderveken's 'Foundations of Illocutionary Logic', the definition of an act's being an 'illocutionary' act is pursued (essentially) in terms of such acts having an 'illocutionary point'; yet no clue is given as to what makes an act's point an 'illocutionary' point: knowledge of what this term means is apparently being presupposed.
EXAMPLE: [~] 'illocutionary act' and 'promising' in Searle's 'Speech Acts'
(3) circularity of causal explanation (highly problematic, but hardly ever instantiated ...)
o [*] circular explanation of the occurrence of ... in terms of natural laws
(4) circular statement of supervenience / constitution / grounding (?)
o 'water is H2O'; 'H2O is water'
That some philosophers neglect the variety of these types of circularity can be seen from the fact that they regularly (!) mingle them up.
[In a later version examples will be given, referring, among other things, to faulty arguments by Grice, Davidson and Quine.]