Some people say that the purpose of science is to provide explanations; this is probably right, because science arises from the pursuit of knowledge, and the pursuit of knowledge arises from “wonder.” The common origin of science and philosophy is humanity’s “curiosity” about this world. It is because we ask “what?” that science came into being, and the original purpose of science was indeed to try to explain how various phenomena can be understood.
The object of scientific explanation is the “explained sentence” — the “Why is it that…?” sentence. So what different types of explained sentences are there?
One distinction divides explained sentences into necessary events and probable events, using the D-N model for the former and the I-S model for the latter. But this division has its shortcomings, because in reality it is often very hard to list all the causes that guarantee an event’s necessary occurrence in this form rather than that one; the line between what is necessary and what is probable is fuzzy.
I think that when discussing scientific explanation, the first thing to note is the syntactic type of the explained sentence. First of all, we must distinguish between explanations of single events and explanations of universal phenomena.
By single events, I mean things like “this piece of ice floats on the water,” “Zhang San has measles,” “a rainbow appeared somewhere this afternoon,” and so on; by universal phenomena, I mean things like “ice always floats on water,” “90% of people who have had close contact with a measles patient will be infected,” “rainbows appear from time to time,” and so on.
The explanations of these two kinds of questions are completely different!
Universal phenomena, such as “ice always floats on water,” can themselves be called “laws.” An explanation of a law can make use of a more “basic” law, and the most basic laws are what are called “scientific laws.” Universal laws and scientific laws are not syntactically different in any substantive way: both take the form “under such-and-such circumstances, such-and-such always (often, possibly) occurs,” except that scientific laws are more basic, more reliable, more generally applicable, and so on.
An explanation of a single event does not necessarily have to trace back to the most fundamental scientific law; using relatively basic laws can already be satisfactory. For example, “Why does this piece of ice float on the water?” can be explained by “Ice always floats on water.” Of course, that is still not entirely satisfactory, but explaining it with “Objects lighter than water in density always float on water” is already pretty close. Further, one can replace water with liquids in general, and quantify the specific state of an object floating on a liquid in terms of density ratios; but for someone who asks “Why does this piece of ice float on the water?” this probably need not be made overly cumbersome.
In addition, when explaining a single event, one usually does not need to provide a necessary proof; it is enough to show that the event’s occurrence is “reasonable” or “lawful.” For example, to answer “Why did Zhang San get measles?” it is enough to give an explanation that makes one believe the occurrence of this event is reasonable and natural. To pursue “Why did Zhang San necessarily (in this way rather than that way) get measles?”—that sort of demand is often excessive. This is especially true for probable events; for example, science can never explain the necessity of “I just now tossed a coin and got heads,” and can only explain that the event of getting heads from a coin toss is reasonable.
The explanation of universal phenomena is quite different. Many people say that scientific explanation is always at once both “argument” and “prediction”; I think that this view applies at most to the explanation of universal phenomena.
Universal phenomena themselves, as “laws,” often appear in the explanation of single events, as when “ice always floats on water” is used to explain “this piece of ice floats on the water.” But if this law itself is not basic enough, or if the person asking “Why does this piece of ice float on the water?” is really asking “Why does ice always float on water?” then such an explanation is not satisfactory enough, and we need to seek an explanation of the “law” itself. Generally speaking, science explains laws by seeking more basic laws; how far one must go in this pursuit depends on the questioner’s requirements.
One may say that as long as one carries out an effective deductive discussion using more basic laws, the explanation is completed—though it may not be fully satisfying. But if one feels that using “ice always floats on water” to explain “this piece of ice floats on water,” or using “objects with lower density always float on water” to explain “ice always floats on water,” is not satisfying enough, then the questioner is in effect engaging in “further questioning.” In other words, what needs explaining is no longer the original question, but an additional demand has been raised. Yet with respect to the question “Why does ice always float on water?” the claim “objects with lower density always float on water” has already completed a full explanation.
Here I have abandoned “being convincing” as a necessary condition for scientific explanation. In fact, scientific explanations are often not satisfactory; in some cases they are even worse than analogical explanations or fairy tales. So let us set a lower bar for what counts as scientific explanation: as long as one uses more “basic” laws to explain laws, or uses “laws” to explain specific events, it can be called an “explanation.” An additional condition is that if the laws and methods used in the explanation are both “scientific” (the wording here is ambiguous; it is impossible to discuss what science really is in just a few paragraphs, so for now we may understand “scientific” as “recognized by the scientific community”), then this explanation is a “scientific explanation.”
When we say that scientific explanation always uses “more basic” (that is, more reliable, more universal) laws to explain laws, then if one traces it back to the end of the line, it will involve “the most basic” laws, namely scientific laws. Of course, which laws count as “scientific laws” is not clearly delineated, and perhaps in the social sciences there simply is no such thing as a “law” at all. For the time being, let us examine only some obvious cases of fundamental laws in the natural sciences—for example, the law of conservation of energy.
How can one scientifically explain something as basic as the law of conservation of energy? I think that, as the saying goes, when an extreme is reached, it must turn back; for these fundamental laws, the only effective and reasonable way to explain them is to reverse direction and make use of concrete real events! That is, use large numbers of “single events” to explain the fundamental law. In fact, it can only be so; unless one resorts to “philosophical explanation” or “religious explanation,” if one wants to explain “why energy is conserved,” the only thing science can say is: “Because a great many experiments and long-term experience have strongly supported the claim that the law of conservation of energy cannot be violated.” — I am afraid there is no better way to explain the most fundamental scientific laws.
In summary, I think the relations among the various objects of scientific explanation are as follows:
┏→law—(explanation)→law—(explanation)→law—(explanation)→specific event┐
↑＿＿＿＿＿＿＿＿＿＿＿(explanation)＿＿＿＿＿＿＿＿＿＿＿＿＿＿↓
If, within a set of explanations, one can complete a cycle from law to event—that is, both deduce from the law to explain that the occurrence of the event is reasonable, and at the same time let the degree of correspondence between the event that actually occurred and the prediction in turn confirm the correctness of the law and the derivation—then that set of explanations is the most successful. Of course, many times we do not need the entire apparatus of explanation, and often it is enough merely to make people believe that “the occurrence of the event is reasonable” or that “the law or regularity is valid.” In addition, in the social sciences, one generally skips the link of basic laws and directly explains one another between specific events and universal regularities.
In the era of Big Science, science itself has formed a huge system. It possesses some relatively fixed basic laws, and the laws support and coordinate one another; numerous observational results and real events accord very well with the laws—at least with relatively few contradictions. It is precisely the effectiveness and reliability of this enormous system that ensure the effectiveness and reliability of scientific explanation.
March 27, 2006
Translated from the Chinese original with AI assistance. The original text is authoritative.
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