  Not all philosophers have agreed that all works of art must be public. In his taxonomy of the fine arts, Bernard Bolzano distinguishes between the arts of the external senses and those of pure thought (1849, 16). The latter arts produce works comprised of complex ideas or thoughts that are not linguistically articulated and that are only directly accessible to the person thinking of them. Bolzano remarks that this feature of the arts of pure thought is a great imperfection. He adds, however, that these arts often play a role in the creation of those works of art, such as statues and songs, that are perceptible to audiences.