Whatever effects cannot be traced to some practical use we might make of them (as we use a plate to eat from or a house to live in), or to some interference with or threat against the ways in which we might act, or to some object practically interesting to us, which they represent—all such effects are necessarily very difficult to explain. There is nothing in the least mysterious, however, about the difficulty of explaining them. The facts required happen to be beyond our present powers of observation. They belong to a branch of psychology for which we have as yet no methods of investigation. It seems likely that we shall have to wait a long while, and that very great advances must first be made in neurology before these problems can profitably be attacked. But however regrettable this may be, there is no justification whatever for the invention of unique faculties and ultimate, analysable, indefinable entities. To say that a thing is unanalysable may be to assert either that it is simple or that we do not know yet how to analyse it. Musical effects, like the effects of forms in general, are inexplicable in the second sense only. To pretend that they are inexplicable in the first sense is mere mystery-mongering. To take two parallel cases, trade booms and fine weather were until recently inexplicable, and are doubtless still in many respects difficult to account for. But no one would pretend that these blessings require us to assume unique _sui generis_ tendencies in economic or meteorological affairs. But the practice of describing the ‘musical faculty’ and the formal effects of the arts in general as _sui generis_ has another cause in addition to intellectual bewilderment. Many people think that to say that a mental activity is unique, or _sui generis_, in some way gives it a more exalted standing than if it were recognised as merely too complicated or too inaccessible to experiment to be at present explained. In part this is a relic of the old opinion that explanation is itself derogatory, an opinion which only those who are, in this respect, uneducated, still entertain. Partly also this preference for ‘unique’ things is due to confusion with the sense in which St Paul’s may be said to be unique. But the experience of ‘seeing stars’ after a bang on the nose is just as ‘unique’ as any act of musical appreciation and shares any exalted quality which such uniqueness may be supposed to confer.