Earl W. Stevick, Adapting and Writing Language Lessons… (1971)
“ The care with which a good PSI course has to be worked out, however, and the delicate balance of one part with another, make tampering by outsiders unadvisable or at least prohibitively expensive. In this appendix, therefore, we shall speak not of 'adaptation,' but of 'augmentation:' assuming that the student will complete a unit of the program exactly as it stands, what can be added to provide additional strength without too much increase in the weight and opacity of the total unit? ”
