No. The inputs are labour and capital, so that's already taken care of. One answer might be "TFP reflects technical knowledge; the more knowledge there is, the

No. The inputs are labour and capital, so that's already taken care of. One answer might be "TFP reflects technical knowledge; the more knowledge there is, the easier it is to generate new knowledge". But you'd have to get into growth macro for the details. Indeed, Romer is the person.