me to the invention of
various objects, and although the blots themselves were altogether
devoid of perfection in any one of their parts, they lacked not
perfection in their movement and circumstance.

50.

Obtain knowledge first, and then proceed to practice, which is born of
knowledge.

[Sidenote: Theory and Practice]

51.

Knowledge is the captain, and practice the soldiers.

52.

The painter who draws by practice and by the {106} eye, without the
guide of reason, is like the mirror, which reflects all the objects
which are placed before it and knows not that they exist.

53.

Many will consider they can reasonably blame me by alleging that my
proofs are contrary to the authority of many men held in great esteem
by their inexperienced judgements: overlooking the fact that my works
are solely and simply the offspring of experience, which is the
veritable master.

54.

They who are enamoured of practice without knowledge are like the
mariner who puts to sea in a vessel without rudder or compass, and who
navigates without a course. Practice should always be based on sound
theory; perspective is the guide and the portal of theory, and without
it nothing can be well done in the art of painting.

[Sidenote: Course of Study]

55.

The youth should first learn perspective, and then the measurements of
every object; he should then copy from some good master to accustom
himself to well-drawn forms, then from nature to acquire confirmation
of the theories he has learnt; then he should study for a time the
works of various masters, and finally attain the {107} habit of putting
into practice and producing his art.

56.

Mathematics, such as appertain to painting, are necessary to the
painter, also the absence of companions who are alien to his studies:
his brain must be versatile and susceptible to the variety of objects
which it encounters, and free from distracting cares. And if in the
contemplation and definition of one subject a second subject
intervenes,--as happens when the mind is filled with an object,--in
such cases he must decide which of the two objects is the more
difficult of definition, and pursue that one until he arrives at
perfect clearness of definition, and then turn to the definition of the
other. And above all things his mind should be like the surface of the
mirror, which shows as many colours as there are objects it reflects;
and his companions should study in the