Circular arguments are often claimed not to be of explanatory value. I argue that this is true primarily as a result of the existence of inverted, 'parody arguments', which take the same circular form, but with every step inverted to yield the opposite conclusion of the opposite premises.
A demonstration that a cyclical universe with a duration of 2 hours will be filled with blue goo: a blue substance consists of tiny entities which live for at least 1+1/2 hours, and duplicate themselves every hour. If at one instance of time, space is filled with these blue entities, then it will be 1 hour later, because they will have continued to exist for the last hour and will now duplicate themselves. These duplicates will still exist another hour later, as they themselves will live for another half hour. But in this universe, the future 2 hours later is the present, which explains why the universe was filled with the blue substance at all.
Parody argument: If at one instance of time, there are no blue creatures in the universe, there won't be any after one hour has passed, because the nonexistence of these blue creatures will propagate itself into the future by one hour. No duplicate blue creatures will come into existence because there were none to begin with. These duplicates will still not exist another hour later, but in this universe, the future 2 hours later is the present, which explains why the universe didn't contain any blue substance at all.
As both the parody argument and the original seem equally logical, there is no way to differentiate them and decide which to believe, other than with a criterion like simplicity.
Circular arguments can also be logically circular even if they refer to something chronologically linear. For example, suppose there was a kind of beetle which lived in a tessellated 'honeycomb' structure along with others of its kind. The following argument suggests that its structure is likely to be cubic:
1) Having a cubic shape is evolutionarily advantageous because it allows each cubic beetle to interlock with the others, which protects it from the cold and predators.
2) This selective pressure will gradually increase the proportion and number of cubic beetles over time.
3) The abundance of cubic beetles explains why it is evolutionarily advantageous to fit in with them as opposed to beetles of some other shape.
This argument also has a parody, but not one of the kind above which is a simple inverse of the original argument:
Suppose there was a kind of animal which lived in a tessellated 'honeycomb' structure along with others of its kind. The following argument suggests that its structure is likely to be tetrahedral: 1) Having a tetrahedral shape is evolutionarily advantageous because it allows each tetrahedral beetle to interlock with the others, which protects it from the cold and predators. 2) This selective pressure will gradually increase the proportion and number of tetrahedral beetles over time. 3) The abundance of tetrahedral beetles explains why it is evolutionarily advantageous to fit in with them as opposed to beetles of some other shape.
Again, the existence of two, apparently equally compelling, arguments for two different conclusions prevents us from being able to determine which one to believe, at least on the basis of these arguments alone. However, unlike the first example, these arguments do suggest something. If the beetles were spherical, then the corresponding argument would cease to be sound, because spherical beetles would not be able to tessellate in the same way. If we modify the original argument to refer to any polyhedra capable of tiling 3-dimensional space with no gaps, it becomes impossible to negate this part of the argument in a way which doesn't weaken it, and therefore much harder to find a symmetric, equally persuasive parody argument.
For this reason, such an argument would be evidence for the existence of tessellating polyhedral beetles of some kind.