EXAMPLES TO CLARIFY THE SCOPE OF (SPEC)

The three examples of speculations noted in section 2— Young's 1802 assumptions about the wave nature of light, Kelvin's assumptions about the molecular nature of the ether, and string theory's assumptions about strings and 10­dimensional spacetime—all satisfy (Spec).

Case 1 Suppose that I have read in a usually but not completely reliable newspaper that there is evidence that 10-dimensional spacetime exists. And suppose the news­paper is right in saying this. Because the newspaper is not completely reliable, I do not know that there really is such evidence, though I have a good reason to believe there is. In accordance with (Spec), if, while “theorizing,” I intro­duce the assumption that such a spacetime exists, I am speculating.

Case 2. Suppose I read in Science magazine, a very re­liable source, that evidence for 10-dimensional spacetime has been discovered, and I use the assumption that 10-dimensional spacetime exists in theorizing in a way that satisfies “theorizing” conditions (a) and (b). In fact, however, unlike Case 1, what Science magazine reports is false: what it took to be evidence is not so, and indeed no evidence exists. According to (Spec), when having read the article I intro­duce the 10-dimensional spacetime assumption into my theorizing, I am speculating. I am justified in believing that there is evidence that 10-dimensional spacetime exists, but in fact there is no such evidence, so I don't know that there is. I believe I am not speculating, I am justified in so believing, but it turns out that I am speculating.

In view of cases such as (1) and (2), the concept of specula­tion I have introduced is a strong one, since it rules some­thing as a speculation in a situation in which the speculator has a good reason to believe there is evidence for the spec­ulation but not enough to know that there is. This doesn't imply that any assumption that I put forth while “theorizing” whose truth I don't know is a speculation for me.

A weaker concept might require only that, given my ep- istemic situation, I am not justified in believing that there is evidence. If I am so justified, I would not be speculating. But suppose I am justified in believing that there is evidence that h, even though there is no such evidence. Then, on this weaker concept of speculation, if I “theorize” using h I am not speculating. Under these circumstances, I am inclined to say that since there is no evidence that h, I am speculating, even though I think there is such evidence and even though I think that I am not speculating.^[23]

I will continue to use the stronger “no knowledge” con­cept. If, like some scientists, you reject speculation, you are not rejecting the “theorizing” use of all assumptions whose truth you don't know, but only the use of assumptions for which you don't know that there is evidence. This permits speculations to cover a broad group of cases, ranging from simple hunches, where you have no idea whether there is evidence or even what would count as evidence, to cases in which in which you have good reason to think that some­thing is (or that there is) evidence but don't know that this is so.

7.