Constancy, change and the ideal form

...the truths of nature are one eternal change—one infinite variety. There is no bush on the face of the globe exactly like another bush;—there are no two trees in the forest whose boughs bend into the same network, nor two leaves on the same tree which could not be told one from the other, nor two waves in the sea exactly alike. And out of this mass of various, yet agreeing beauty, it is by long attention only that the conception of the constant character—the ideal form—hinted at by all, yet assumed by none, is fixed upon the imagination for its standard of truth.

(Modern Painters I)

Knowing and Seeing

And all the early works, whether of nations or of men, show, by their want of shade, how little the eye, without knowledge, is to be depended upon to discover truth. The eye of a Red Indian, keen enough to find the trace of his enemy or his prey, even in the unnatural turn of a trodden leaf, is yet so blunt to the impressions of shade, that Mr. Catlin mentions his once having been in great danger from having painted a portrait with the face in half-light, which the untutored observers imagined and affirmed to be the painting of half a face. Barry, in his sixth lecture, takes notice of the same want of actual sight in the early painters of Italy. "The imitations," he says, "of early art are like those of children—nothing is seen in the spectacle before us, unless it be previously known and sought for; and numberless observable differences between the age of ignorance and that of knowledge, show how much the contraction or extension of our sphere of vision depends upon other considerations than the mere returns of our natural optics." And the deception which takes place so broadly in cases like these, has infinitely greater influence over our judgment of the more intricate and less tangible truths of nature. We are constantly supposing that we see what experience only has shown us, or can show us, to have existence, constantly missing the sight of what we do not know beforehand to be visible: and painters, to the last hour of their lives, are apt to fall in some degree into the error of painting what exists, rather than what they can see. I shall prove the extent of this error more completely hereafter. 

(Modern Painters I)

On Seeing and Attention

...unless the minds of men are particularly directed to the impressions of sight, objects pass perpetually before the eyes without conveying any impression to the brain at all; and so pass actually unseen, not merely unnoticed, but in the full, clear sense of the word, unseen.

...a man may receive impression after impression, and that vividly and with delight, and yet, if he take no care to reason upon those impressions and trace them to their sources, he may remain totally ignorant of the facts that produced them;

How many people are misled, by what has been said and sung of the serenity of Italian skies, to suppose they must be more blue than the skies of the north, and think that they see them so; whereas, the sky of Italy is far more dull and gray in color than the skies of the north, and is distinguished only by its intense repose of light. And this is confirmed by Benvenuto Cellini, who, I remember, on his first entering France, is especially struck with the clearness of the sky, as contrasted with the mist of Italy. And what is more strange still, when people see in a painting what they suppose to have been the source of their impressions, they will affirm it to be truthful, though they feel no such impression resulting from it. Thus, though day after day they may have been impressed by the tone and warmth of an Italian sky, yet not having traced the feeling to its source, and supposing themselves impressed by its blueness, they will affirm a blue sky in a painting to be truthful, and reject the most faithful rendering of all the real attributes of Italy as cold or dull. 

The exceeding importance of truth

Nothing can atone for the want of truth, not the most brilliant imagination, the most playful fancy, the most pure feeling, (supposing that feeling could be pure and false at the same time;) not the most exalted conception, nor the most comprehensive grasp of intellect, can make amends for the want of truth, and that for two reasons; first, because falsehood is in itself revolting and degrading; and secondly, because nature is so immeasurably superior to all that the human mind can conceive, that every departure from her is a fall beneath her, so that there can be no such thing as an ornamental falsehood. All falsehood must be a blot as well as a sin, an injury as well as a deception.

(Modern Painters vol 1)

Ideas peculiar to things

It is self-evident that when we are painting or describing anything, those truths must be the most important which are most characteristic of what is to be told or represented. Now that which is first and most broadly characteristic of a thing, is that which distinguishes its genus, or which makes it what it is. For instance, that which makes drapery be drapery, is not its being made of silk or worsted or flax, for things are made of all these which are not drapery, but the ideas peculiar to drapery; the properties which, when inherent in a thing, make it drapery, are extension, non-elastic flexibility, unity and comparative thinness. Everything which has these properties, a waterfall, for instance, if united and extended, or a net of weeds over a wall, is drapery, as much as silk or woollen stuff is. So that these ideas separate drapery in our minds from everything else; they are peculiarly characteristic of it, and therefore are the most important group of ideas connected with it.

(Modern Painters vol 1, ΙΙ.Ι.ΙΙΙ,5)