THE LOCH NESS MONSTER AND SEVERED HEAD CASES

Two objections to the definitions of section 4 will now be considered.

There is a well-known photograph taken by a London surgeon in 1934 which purports to depict the Loch Ness monster.^[14] Even if the existence of the monster is very improbable despite the photograph, isn’t the ex­istence of the photograph evidence that the monster exists? If so there is a violation of the condition for potential evidence that p(h/e) be high.

We are being asked to consider the claim that

(1) The existence of this photograph which purports to depict the Loch Ness monster is evidence that the monster exists.

Someone who believes that (1) is true might defend it by providing in­formation about the surgeon who took the picture, from what position, at what time of day, and so on. He might also point out how the camera used works and that photographs are generally reliable; that is, usually when a photograph depicts what seems clearly to be X and the photogra­pher has not made efforts to be deceptive, then an X exists.^[15] But if this is how he defends (1) then, I think, he should not accept the claim that the existence of the monster is very improbable despite the photograph. On the contrary, he should believe that it is probable. (Indeed, this is what Sir Peter Scott claimed about later photographs taken in 1972.) New infor­mation can cancel the negative effects of background information. Even if the existence of the Loch Ness monster is improbable on the background information, a suitable photograph can make its existence very probable.

However, two other situations are possible. First, we may not know the reliability of the photographer, the conditions under which the pho­tograph was taken, or indeed whether it is a genuine photograph (rather than a clever drawing).

The importance of the subjective concept of evidence should not be minimized here. A question such as “Is there any evidence that there is a Loch Ness monster?” might be understood as “Is there anything that people take to be evidence that the monster exists?” To which the answer is: emphatically yes! It is not that those who believe that the monster exists are unable to appeal to any facts as their reason for so believing. Quite the reverse. The existence of this photograph, among other things, is their evidence.

Finally, when the probability of h given e is low, although e is not evi­dence that h is true it can be evidence that h may be true (or that h is pos­sible). One might claim that the existence of the surgeon's photograph is evidence that there may be a monster. The fact that Joe is one of 50 finalists in the state lottery is not evidence that he will win $1 million— that is too strong a claim to make. But it can be evidence that he may win $1 million or that his winning is a possibility. The fact that Bob is playing one round of Russian roulette is not evidence that he will die but that he may die, that his dying is a possibility. Such evidence claims, although different from the ones we have been considering, can be understood, I think, by altering the concept of potential evidence so as to require not high probabilities but non-negligible ones.

e is evidence that h may be true (or that h is possible) if and only if (a) e is true;

(b) e does not entail h; (c) the probability of h given e is not negligible; (d) the probability that there is an explanatory connection between h and e, given h and e, is not negligible.

The fact that (e) Bob is playing one round of Russian roulette is evidence that h may be true, where h is the hypothesis that Bob will die. This is so since the probability of h, given e, is not negligible; and given that h and e are both true, the probability is not negligible that there is an explanatory con­nection between Bob's dying and his playing one round of Russian roulette.

The second objection to definitions of section 4 will be dealt with more briefly. We saw that the requirement of an explanatory connection be­tween e and h for e to be veridical evidence that h allows us to preclude certain unwanted cases. In view of the following gruesome example, how­ever, it may be wondered whether this requirement is too strong.

Henry drops dead from a heart attack. Afterward his head is severed by a fiendish decapitator.^[16] Isn't the fact that his head has been severed from his body veridical evidence that Henry is not living, even though there is no explanatory connection between his decapitation and his not being alive? If so the explanatory requirement is not necessary for veridical (or potential) evidence.

The latter conclusion is too hasty. There are various reasons one may not be alive, not all of which need be reasons for which one died. Anyone whose head has been severed from his body is not alive because, among other things, his brain is unable to receive oxygen from the rest of his body. Consider an analogous case. Tom's TV set is not working because one of the tubes burned out. Later Tom accidentally drops the set breaking the remaining tubes. Now among the reasons the set is not working is that all the other tubes are broken (although this is not among the reasons that it stopped working in the first place). There is an explanatory connection be­tween the fact that these other tubes are broken and the fact that the set is not working; indeed, the former is veridical evidence that the latter is true.

7.