The Wealth of Nations by Part 5 Chapter 1 Page 202

evidently derived from a fund altogether independent of their success and reputation in their particular professions.

In some universities the salary makes but a part, and frequently but a small part, of the emoluments of the teacher, of which the greater part arises from the honoraries or fees of his pupils.

The necessity of application, though always more or less diminished, is not in this case entirely taken away. Reputation in his profession is still of some importance to him, and he still has some dependency upon the affection, gratitude, and favourable report of those who have attended upon his instructions; and these favourable sentiments he is likely to gain in no way so well as by deserving them, that is, by the abilities and diligence with which he discharges every part of his duty.