IN this paper I wish to examine two theses about seeing,and then suggest a third. The twotheses are advanced to account for the late Professor Hanson calls controversy in research science.1 Such conflicts arise when there is a disagreement about the data although all the data are in. Hanson's examples are (pp. 4-5): (1) two microbiologists one of whom claims to have discovered a new cell organ while the other-examining the same slide-attributes he sees to a faulty staining technique. And (2) Tycho Brahe and Kepler watching the sun at dawn. Of these astronomers Hanson says-and this is thesis I-that they do not see the same thing, but also-and this is thesis II-that they both see the sun but do not mean the same thing by sun . Obviously, thesis II may be understood either as an addition or as an alternative to thesis I. What both theses are intended to account for are the facts that the first microbiologist will embark on a new research project while the second will not, aind that Brahe and Kepler will look for different paths of different heavenly bodies. Both theses are false if they are understood as theses about seeing-and this is how Hanson presents them-but his claims in defence of thesis I are mostly true when they are understood as claims about observing-and that, I suspect, is how he meant them. Hanson's argument in defence of the first thesis may be summarized as follows. Consider two normal observers, a physicist and a layman, who are looking at an X-ray tube, are paying attention, have an unobstructed view and good light, etc. If we ask the physicist, what do you see now ? , he is in a position to reply, I see an X-ray tube . The layman, in contrast, could only reply, a glass-and-metal gadget or a complicated light bulb . Of course, the layman might have overheard the physicist's reply and believed it, then he too could answer, an X-ray tube ; but for the sake of simplicity let us assume that he did not and thus cannot. Hanson then raises the question whether the physicist and the layman see the same thing and concludes that they do and they do not. They are visually aware of the same thing but the ways