CORRECT EXPLANATION
To proceed, I will introduce the idea of content. Consider sentences such as:
(1) The reason John got sick is that he ate contaminated fish.
(2) The penalty for trespassing is that the person convicted will be drawn and quartered.
These sentences contain content-nouns (in italics) together with that-clauses (or more generally nominals) that give content to the noun. They can be used in forming what I call content-giving sentences such as the two above. Contrast these sentences with the following:
(3) The reason John got sick is easy to grasp.
(4) The penalty for trespassing is cruel and unusual.
These sentences do not say what the reason or the penalty is. They do not give a content to the noun in question. Sentence
16. Those familiar with my previous work on “correct explanation” in The Nature of Explanation may wish to briefly review material in sections 5-7 of this chapter or turn directly to section 8.
(1), but not sentence (3), contains an answer to the question “Why did John get sick?” by giving the reason. Sentence
(2), but not sentence (4), contains an answer to the question “What is the penalty?” by giving the penalty. I will say that sentence (1) is a content-giving sentence with respect to the question “Why did John get sick?” And sentence (2) is a content-giving sentence with respect to the question “What is the penalty for trespassing?”
A question such as “Why did John get sick?” presupposes various things—e.g., that John exists (or existed), that John got sick, and that John got sick for a reason. A complete presupposition of a question is given by a sentence that entails all and only the presuppositions of that question. Of the three examples just given, only the last is a complete presupposition of the question “Why did John get sick?” viz.,
(5) John got sick for a reason.
This sentence can be transformed into the following complete answer form for the question “Why did John get sick?”
(6) The reason that John got sick is----
by dropping “for a reason” in (5) and putting the expression “the reason that” at the beginning and “is” followed by a blank at the end, to yield (6).
I will now say that p is a complete content-giving sentence with respect to a question Q if p is a content-giving sentence with respect to Q, p is a sentence obtained from a complete answer form for Q by filling in the blank, and p is not a presupposition of Q. Finally, Q will be said to be a content-question if and only if there is a sentence that is a complete content-giving sentence with respect to Q. By these definitions, (1) is a complete contentgiving sentence with respect to the content-question “Why did John get sick?”If Q is a content-question (whose indirect form is q), and p is a complete content-giving sentence with respect to Q, then p provides an explanation of q. Thus, (1) provides an explanation of why John got sick. More generally, any explanation that is offered is, or can be transformed into, one that answers some content-question by supplying a complete content-giving sentence with respect to that question.
With these concepts, we can provide a simple condition for the correctness of an explanation:
(7) If p is a complete content-giving sentence with respect to Q, then p provides a correct explanation of q if and only if p is true.
Since (1) is a complete content-giving sentence with respect to the content-question:
Q: Why did John get sick?
(1), assuming it is true, provides a correct explanation of why John got sick.
Condition (7) for correctness of an explanation has more bite than it might seem. Compare (1) with:
(8) John ate contaminated fish.
Even if (8) is true, this will not guarantee that (8) provides a correct explanation of why John got sick. (He might not have gotten sick from the contaminated fish but from something else.) (8) is not a complete content-giving sentence with respect to Q. By contrast, if (1) is true, then, since it is a complete content-giving sentence with respect to Q, it provides a correct explanation of q, in accordance with condition (7).
A correct explanation may not be a good one, nor a good one correct.
Goodness in explanations is a broader concept than correctness, and, unlike the latter, is context dependent. Whether (1), even if true, provides a good explanation of why John got sick depends on the “appropriateness” of the answer it provides, which is determined by the knowledge and interests of those for whom the answer is provided. For John's doctor who is inquiring simply about what if anything John did that produced the sickness, (1) may be appropriate. For a medical researcher who wants to know much more—e.g., how contaminated fish could have produced John's sickness—(1) is not good enough at all. Conversely, an explanation may be a good one, even though it is incorrect. Explanations such as the Ptolemaic and Newtonian ones of the observed motions of the planets, though incorrect, may be regarded as good ones on grounds of historical importance, or of this together with their comprehensiveness, precision, and predictive successes.6.