What is art?

'There is one indubitable indication distinguishing real art from its counterfeit, namely, the infectiousness of art...If a man is infected by the authors condition of soul, if he feels this emotion and this union with others, then the object which has effected this is art; but if there be no such infection, if there be not this union with the author and with others who are moved by the same work--then it is not art. And not only is infection a sure sign of art, but the degree of infectiousness is also the sole measure of excellence in art''