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The form of perception and the object of perception

Mark A. Hurt MD


Let's visit a thorny subject in pathology (that has wider implications in philosophy in general). Perhaps the easiest way to state it is that it is the problem of understanding the difference between the form of perception and the object of perception.

At the risk of appearing to lapse into subjectivity, here is a common example: you and your colleague are looking through a multi-headed microscope at a melanocytic lesion stained in one section with H&E and another with Melan-A.

You observe that the the lesion is horizontally oriented, compound, contains a junctional component that extends beyond the dermal component peripherally in both directions, and with Melan-A, the suprapapillary plates are spared consistently throughout the lesion. Because the dermal component is very superficial, you conclude that this is a Clark's (lentiginous melanocytic) nevus.

But, your colleague counters that the features mean that the lesion is “dysplastic” and is “on its way” to becoming a melanoma.

The discussion the devolves into both agreeing that all knowledge is subjective.

Who's right?

Before I answer, go to case #10 of the “difficult opinion cases” on this website. It is found at the following link:


Notice how the reviewers can look at the same data, the object, and come to different conclusions by the same means, the form of perception, which, in this case, consists of H&E sections and a few immunostains as perceived from images taken through a photo-microscope.

It is the object, the lesion, perceived by the subject, the reviewer, via a given means, sections stained by standard methods.

Why are there differences of opinion about the object? Clearly, we are all looking at the same object, but we differ in our opinions about it. Do we differ because the object is different for each of us? No, it is the same object. In fact, in case 10, the same object is perceived through different means: H&E is one means, Melan-A is another means, HMB-45 another, and Ki-67 still another.

The differences of opinion are accounted for by reference to the fact that each of us has come to our conclusions about the nature of the object because of our different training backgrounds, our different understandings of how to apply language to a given lesion, and our own experience in dealing with similar lesions. This does not mean that knowledge is subjective, but it does mean that for each of us to understand each other we must have clear definitions and methods that do not vary from case to case.

In the first case above, neither is right. Knowledge is not subjective unless one refuses to conform to objective definitions based on empirical observation.

Regardless of what any of us says, the lesion behaves according to its natural history. Our job is to discover what that natural history actually is.


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