The question is most strikingly illustrated by the case of a given work and a forgery or copy or reproduction of it. Suppose we have before us, on the left, Rembrandt's original painting Lucretia and, on the right, a superlative imitation of it. We know from a fully documented history that the painting on the left is the original; and we know from X-ray photographs and microscopic examination and chemical analysis that the painting on the right is a recent fake. Although there are many differences between the two - for example, in authorship, age, physical and chemical characteristics, and market value - we cannot see any difference between them; and if they are moved while we sleep, we cannot then tell which is which by merely looking at them. Now we are pressed with the question whether there can be any aesthetic difference between the two pictures; and the questioner's tone often intimates that the answer is plainly no, that the only differences here are aesthetically irrelevant.

We must begin by inquiring whether the distinction between what can and what cannot be seen in the pictures by "merely looking at them" is entirely clear. We are looking at the pictures, but presumably not "merely looking" at them, when we examine them under a microscope or fluoroscope. Does merely looking, then, mean looking without the use of any instrument? This seems a little unfair to the man who needs glasses to tell a painting from a hippopotamus. But if glasses are permitted at all, how strong may they be and can we consistently exclude the magnifying glass and the microscope? Again, if incandescent light is permitted, can violet-ray light be ruled out? And even with incandescent light, must it be of medium intensity and from a normal angle, or is a strong raking light permitted? All these cases might be covered by saying that "merely looking" is looking at the pictures without any use of instruments other than those customarily used in looking at things in general. This will cause trouble when we turn, say, to certain miniature illuminations 'or Assyrian cylinder seals that we can hardly distinguish from the crudest copies without using a strong glass. Furthermore, even in our case of the two pictures, subtle differences of drawing or painting discoverable only with a magnifying glass may still, quite obviously, be aesthetic differences between the pictures. If a powerful microscope is used instead, this is no longer the case; but just how much magnification is permitted? To specify what is meant by merely looking at the pictures is thus far from easy; but for the sake of argument, let us suppose that all these difficulties have been resolved and the notion of "merely looking" made clear enough. . .