We investigate how C. S. Peirce's theory of metaphor can provide us with an insight into concept formation. It is interesting that Peirce does not write much about the metaphor; still his suggestion that the basic mechanism of metaphor is that of parallelism is very interesting. This seems to suggest that metaphor is important to Peirce however, not as a poetical adornment but as a special branch of abduction and as a basic esthetic element that pushes science forward towards the esthetic ideal: growth in concrete reasonableness. (Bent Sørensen and Torkild Thellefsen)