Although it is distinct from induction and deduction, abduction is often mistaken for them. The initial stage of abduction, or novel hypothesis abduction, has 2 components. The first concerns providing novel hypotheses that explain the pattern of data; the second suggests that the novel hypothesis should be accepted to the extent that it is the best available hypothesis. The second component is known as inference to the best explanation. Others have shown how novel hypothesis abduction provides an important type of reasoning for generating novel hypotheses. Our concern is with evaluating already formed abductions to determine which is best, using inference to the best explanation in connection with theories. We call this competing theories abduction. Competing theories abduction suggests that theories should be evaluated in relation to other theories rather than in isolation, as suggested by some philosophers and psychologists. In psychology this is demonstrated in connection with 2 widely accepted forms of relativism: the logical possibilities view and unique standards relativism.