scientific in­ vestigations seems to be essential to the views of these men. Each would further hold that transitions from one scientific tradition to another force radical changes in what is observed, in the meanings of the terms employed, and in the metastandards involved. They would claim that total replace­ ment, not reduction, is what does, and should, occur during scientific revolutions. I argue that the proposed arguments for radical observational variance, for radical meaning variance, and for radical variance of regulative standards with respect to scientific transitions all fail. I further argue that these positions are in themselves implausible and methodologically undesirable. I sketch an account of the rationale of scientific change which preserves the merits and avoids the shortcomings of the approach of radical meaning variance theorists.