The condition of necessity which a judgement of taste asserts is the Idea of a common sense

If judgements of taste (like cognitive judgements) had a definite objective principle, then the person who lays them down in accordance with this latter would claim an unconditioned necessity for his judgement. If they were devoid of all principle, like those of the mere taste of sense, we would not allow them in thought any necessity whatever. Hence they must have a subjective principle which determines what pleases or displeases only by feeling and not by concepts, but yet with universal validity.

But such a principle could only be regarded as a common sense, which is essentially different from common Understanding which people sometimes call common sense (sensus communis);