To such an extent does nature delight and abound in variety that among her trees there is not one plant to be found which is exactly like another; and not only among the plants, but among the boughs, the leaves and the fruits, you will not find one which is exactly similar to another.
In whatever system where the weight attached to the wheel should be the cause of motion of the wheel, without any doubt the center of the gravity of the weight will stop beneath the center of its axle. No instrument devised by human ingenuity, which turns with its wheel, can remedy this effect. Oh, speculators about perpetual motion, how many vain chimeras have you created in the like quest. Go and take you place with the seekers after gold.
The vivacity and brightness of colors in a landscape will never bear any comparison with a landscape in nature when it is illumined by the sun, unless the painting is placed in such a position that it will receive the same light from the sun as does the landscape.
It reflects no great honor on a painter to be able to execute only one thing well -- such as a head, an academy figure, or draperies, animals, landscapes, or the like -- in other words, confining himself to some particular object of study. This is so because there is scarcely a person so devoid of genius as to fail of success if he applies himself earnestly to one branch of study and practices it continually.
Shadow is the obstruction of light. Shadows appear to me to be of supreme importance in perspective, because, without them opaque and solid bodies will be ill defined; that which is contained within their outlines and their boundaries themselves will be ill-understood unless they are shown against a background of a different tone from themselves.
There is nothing that deceives us more than our own judgment when used to give an opinion on our own works. It is sound in judging the work of our enemies but not that of our friends, for hate and love are two of the most powerfully motivating factors found among living things.
All our knowledge hast its origins in our perceptions … In nature there is no effect without a cause … Experience never errs; it is only your judgments that err by promising themselves effects such as are not caused by your experiments … Science is the observation of things possible, whether present or past; prescience is the knowledge of things which may come to pass.
Although the poet has as wide a choice of subjects as the painter, his creations fail to afford as much satisfaction to mankind as do paintings... if the poet serves the understanding by way of the ear, the painter does so by the eye, which is the nobler sense.
One painter ought never to imitate the manner of any other; because in that case he cannot be called the child of nature, but the grandchild. It is always best to have recourse to nature, which is replete with such abundance of objects, than to the productions of other masters, who learnt everything from her.