But because we have once accustomed ourselves to combine in conception, under the name of theory of Art, or simply Art, the branches of knowledge (which may be separately pure sciences) necessary for the practice of an Art, therefore it is consistent to continue this ground of distinction, and to call everything Art when the object is to carry out the "doing" (being able), as for example, Art of building; Science, when merely knowledge is the object; as Science of mathematics, of astronomy.

That in every Art certain complete sciences may be included is intelligible of itself, and should not perplex us.
But still it is worth observing that there is also no science without a mixture of Art.

In mathematics, for instance, the use of figures and of algebra is an Art, but that is only one amongst many instances.

The reason is, that however plain and palpable the difference is between knowledge and power in the composite results of human knowledge, yet it is difficult to trace out their line of separation in man himself.
2.

DIFFICULTY OF SEPARATING PERCEPTION FROM JUDGMENT.
(ART OF WAR.) All thinking is indeed Art.