The threshold model of scientific change and the continuity of scientific knowledge

The continuity thesis of the Pozna school threshold model of the growth of scientific knowledge is considered in the light of the example of Van der Waals' and Boyle-Mariotte's laws. It is argued — using both traditional logical means and the structuralist reconstruction of the example — that the continuity thesis does not hold.A distinction between a historical and a systematic point of view is introduced and it is argued that the continuity thesis of the threshold model presupposes the systematic point of view. However, looking at matters from the systematic point of view need not yield the original theory, looked at from the historical point of view. Applied to the case of Van der Waals/Boyle-Mariotte laws, it turns out that the latter law is not a true idealizing special case of the former, contrary to the continuity thesis.