Definitions

Cogency

[koh-juhn-see]
An argument is cogent if and only if the truth of the argument's premises would render the truth of the conclusion probable (i.e., the argument is strong), and the argument's premises are, in fact, true. Cogency can be considered inductive logic's analogue to deductive logic's "soundness." As an example, consider the following.

Without looking, Lauren pulled out 100 marbles from a bag; 95 of the marbles Lauren pulled out were red.
Therefore, the next marble Lauren pulls out from the bag will be red.

The truth of the premises would, indeed, make the conclusion probable. Therefore, this argument is strong. If the premises are, in fact, true, then the argument is also cogent.

"Probable"

There is no standard of how likely an event must be for it to be called "probable." Just as there are degrees of probability, one can also speak of degrees of cogency. The degree of an argument's cogency, then, is a function of the argument's strength. In the above example, Lauren pulling out a 96th marble that turns out to be red would make the conclusion even more likely, and therefore the argument stronger. Note that this feature of cogency is a disanalogy from deductive logic's "validity," since a deductive argument can be either valid or invalid and nothing in between.

Good argument

For an argument to qualify as a good argument, it is necessary that the argument be sound or cogent. But soundness or cogency need not be sufficient for a good argument. For example, a circular argument can be a sound argument, but it is certainly not good. Similarly, a cogent argument might nonetheless beg the question. In order for a cogent argument to be a good argument, the premises of the argument would have to satisfy additional conditions, such as being acceptable in the context of discussion, and being relevant to the conclusion.