奎因哲学词条：必然性

（《奎因短文集：一本不拘泥于分类学标准的哲学词典》，译者：翟玉章）

Necessity

必然性

【“must”用法的奇特性。对形而上学必然性的反对：必然性和可能性可以互相定义，但无法给予独立的解释。认识论意义上的必然性。关于自然的真理，从永恒的角度看，既没有必然真理也没有偶然真理，它们都是平等的。数学真理给人的必然性感觉来自我们不愿过分晃动科学系统的谨慎性策略。在日常交流中，我们倾向于把那些对话各方都同意的语句以及它们的逻辑后承称为必然的。】

本文提到的词条：必然性、屈折变化、否定、预言。

'Must', we are told, implies 'is'. Whatever is necessarily the case is the case. Yet I say "He must be halfway home" precisely to allow for my missing my guess and his not being halfway home. Otherwise I would say "He's halfway home" flat out. Clearly something must give, and what must give is 'must'. The word may express necessity half the time, but half the time it connotes precisely the lack of necessity, or the lack anyway of certainty. 'Must' is a law unto itself, if 'law' is the word I want. See INFLECTIONand NEGATION.

我们被告知，“一定”（must）蕴涵了“是”（is）。如果一件事必然是如此这般的，那么它是如此这般的。然而，当我说“他一定在回家的路上”（He must be halfway home）时，恰好是允许自己猜错的（即允许他并没在回家的路上）。如果我确有把握，会直接说“他在回家的路上”（He's halfway home）。从不那么有把握到很有把握，我的语句明显少了某种东西，那就是“一定”（must）这个词。这个词有很多时候被用来表达必然性，但也有很多时候恰好被用来表达必然性（或确实性）的缺乏。“must”在用法上完全是不拘一格的。参见屈折变化和否定。

GOOGLE: We are told that "must" implies "is". If something must be so-and-so, then it is so-and-so. However, when I say "He must be halfway home", I am allowing myself to guess wrong (i.e. allowing that he is not on his way home). If I am really sure, I will just say "He's halfway home". From not so sure to very sure, my sentence is obviously missing something, namely the word "must". There are many times when this word is used to express necessity, but there are also many times when it is used to express the lack of necessity (or certainty). "Must" is completely eclectic in its usage. See INFLECTION and NEGATION.

Leaving 'must' then to its fun and games, let us come to grips with necessity as such. It is not easy. A leaf that-latter {140} day philosophers have taken from Leibniz's book explains necessity as truth in all possible worlds. Whatever clarity can be gained from explaining necessity in terms of possibility, however, can be gained more directly: a sentence is necessarily true if it is not possibly false. 'Necessarily' means 'not possibly not'. And we can equally well explain possibility in terms of necessity: 'possibly' means 'not necessarily not'. We understand both adverbs or neither. Each is perhaps the more useful in that it affords an explanation of the other, but we must cast about still for outside help.

让我们把“must”留给娱乐和游戏，而来处理必然性本身吧。这并不容易。后世哲学家从莱布尼兹著作中的某处找到一种解释：必然性就是在所有可能世界中都成立的真理性。其实，用可能性（而不是可能世界）来解释必然性是更直接的，而且获得的清晰性并不稍减：一个语句是必然真的，如果它不可能为假。“必然”就是“不可能并非”。同样地，我们也可以用必然性来解释可能性：“可能”就是“不必然并非”。这两个副词，“必然”和“可能”，我们要么都理解，要么都不理解。每一个都是有用的，因为它可以用来解释另一个，但为了避免循环解释，我们必须到外面寻找对其中至少一个的独立解释。

GOOGLE: Let’s leave the “must” to fun and games and deal with necessity itself. It's not easy. Later philosophers found an explanation somewhere in Leibniz's work: necessity is truth that holds in all possible worlds. In fact, it is more straightforward to explain necessity in terms of possibility (rather than possible worlds), and the clarity gained is no less: a statement is necessarily true if it is not possibly false. "Necessarily" means "not possibly not". Similarly, we can also use necessity to explain possibility: "possibly" means "not necessarily not." We either understand these two adverbs, "necessarily" and "possibly," or neither. Each is useful because it can be used to explain the other, but to avoid circular explanation we must look outside for independent explanation of at least one of them.

David Hume despaired, two centuries ago, of distinguishing between what is necessarily so and what just so happens. It is commonly said that the truths of mathematics and the laws of nature hold necessarily, along with all their logical consequences. However, this only pushes the problem back. Which of the truths about nature are to count as laws of nature, rather than as just so happening? Well, we are told, they should be general. No, this does not help; even the most typical singular sentences are equivalent, trivially, to general ones. 'Garfield was born in Orange' is equivalent to the generality 'Everyone was either born in Orange or is other than Garfield'. The further requirement is then proposed that a law of nature single out no specific object, such as Orange or Garfield. But the trouble with this requirement is that it would disqualify the laws of geology, which cite our planet, and the laws that hinge on specifying the sun and the solar system. It would leave us with the broadest laws of physics, and few occasions to apply the adverb 'necessarily'.

两个世纪以前，大卫·休谟就对区分必然如此和碰巧如此感到绝望。人们常说，数学真理和自然规律，以及它们的逻辑后承，是必然成立的。但这只是把问题延后而已。我们可以追问：哪些关于自然的真理可以被称为自然规律（而不是对碰巧发生的事情的描述）？我们被告知，自然规律应该是概括性的。但这是无济于事的；任何一个寻常不过的单独句，也都有着显而易见的有与之等价的概括句。“加菲尔德出生在奥兰治”就与概括句“每个人要么出生在奥兰治要么是加菲尔德以外的人”[1]是等价的。于是进一步的要求提出来了：自然规律不能是关于特定对象（如奥兰治或加菲尔德）。但这个要求会取消地学规律的规律地位，因为它们就是关于我们这个星球的，也会取消那些提到太阳和太阳系的规律的规律地位。这样一来，有资格被称为规律的，将只剩下最普遍的物理规律，使用副词“必然”的机会将少得可怜。

Two centuries ago, David Hume despaired of distinguishing between what must be so and what happens to be so. It is often said that mathematical truths and natural laws, as well as their logical consequences, are necessary. But this only postpones the problem. We can ask: What truths about nature can be called laws of nature (as opposed to descriptions of what happens to be the case)? We are told that the laws of nature are supposed to be general. But this is no use; for every ordinary singular sentence, there is also an obvious equivalent general sentence. "Garfield was born in Orange" is equivalent to the general sentence "Everyone is either born in Orange or is someone other than Garfield." A further requirement then arises: the laws of nature cannot be about specific objects (such as Orange or Garfield). But this requirement would cancel the law status of geological laws, since they are about our planet, and would also cancel the law status of those laws that refer to the sun and solar system. In this way, only the most general physical laws will be left that qualify to be called laws, and the chances of using the adverb "necessarily" will be very few.

Hume was right, I hold, in discrediting metaphysical necessity. Laws of nature differ from other truths of nature only in how we arrive at them. A generality that is true of nature qualifies as a law, I suggest, if we arrive at it inductively or hypothetico-deductively (see PREDICTION) rather than by the sort of trickery seen in the Garfield example. Sub specie aeternitatis there is no necessity and no contingency; all truth is on a par.

我认为，休谟对形而上学必然性的反对是正确的。至于自然规律和其他自然真理的区别，仅仅在于我们获得它们的方式不同。我的建议是：一个关于自然的真概括是一条规律，如果我们得到它的方法是归纳或假说演绎法（见预言），而不是刚才在加菲尔德的例子中看到的那种戏法。但从永恒的角度看，既没有必然的真理，也没有只是巧合的真理，所有真理都是平等的。

GOOGLE: I think Hume is right to object to metaphysical necessity. As for the difference between natural laws and other natural truths, it is only in the way by which we obtain them. My suggestion is this: a true generalization about nature is a law if the way by which we arrive at it is induction or hypothetical-deduction (see PREDICTION), rather than the kind of trickery we just saw in Garfield's example. But from an eternal point of view, there are neither necessary truths nor truths by mere coincidence. All truths are equal.

{141} The adverb 'necessarily' is much more frequent in daily discourse than called for by laws of nature, let alone metaphysical necessity. In this vernacular use the human element that I have ascribed to law is more marked; necessity commonly so called comes and goes from occasion to occasion. In the course of a discussion we are apt to attach this adverb to a sentence that can be seen to follow from something on which we and our interlocutor are agreed, in contrast to the points that are still moot. In expository writing we are apt to attach it to a sentence that clearly follows from something farther up the page, in contrast to what is conjecture or still in the course of being proved.

在日常交流中，“必然”这个副词出现的频率远比自然规律或形而上学必然性所要求的高。这个词的日常用法中的人为因素，要比“规律”这个词更加明显。通常所谓的必然性是随着场合而出现和消失的。在一场讨论中，我们倾向于把必然性赋予这样的语句：它为我们和对话者所一致同意的一些语句所蕴涵。与这样的语句形成对比的是那些真理性尚无定论的语句。在阐释性文字中，我们倾向于把必然性赋予这样的语句：它明显为前面已经承认为真的一些语句所蕴涵。与这样的语句形成对比的是那些真理性仍处于猜想阶段的语句，或其真理性仍有待证明的语句。

GOOGLE：In everyday communication, the adverb "necessary" occurs far more frequently than the laws of nature or metaphysical necessity would require. The human element is more obvious in everyday usage of the word than in the word "law." What is usually called necessity appears and disappears according to the occasion. In a discussion, we tend to attribute necessity to sentences that are entailed by some sentences on which we and our interlocutors agree. In contrast to such statements are statements whose truth is inconclusive. In expository writing, we tend to attribute necessity to sentences that are clearly entailed by some previous sentences admitted to be true. In contrast to such statements are statements whose truth remains in the conjectural stage, or whose truth remains to be proven.

There remains a loose end that wants picking up. Two paragraphs back I noted the purported necessity of the truths of mathematics and the laws of nature, and proceeded to dispose of the laws of nature. But mathematical necessity calls for quite another account, hinging on something in the theory of evidence called holism, over which let us now pause for a while. The point of holism, stressed by Pierre Duhem eighty years ago, is that the observable consequence by which we test a scientific hypothesis is ordinarily not a consequence of the hypothesis taken by itself; it is a consequence only of a whole cluster of sentences, among which the hypothesis in question merely happens to be the one in question. To put it in the terms of the piece on PREDICTION, the hypothesis does not by itself imply an observation categorical.

还有一个问题需要解决。后退到两段前，我曾经提到数学真理和自然规律的所谓必然性，但随后我只讨论了自然规律的必然性问题。现在让我们回到数学真理的必然性问题。对它的讨论要用到被称为整体主义的证据理论。让我先就整体主义说两句。整体主义80年前就为皮埃尔·迪昂所强调，其要点是，我们用来检验一个科学假说的观察结果，通常并不为这个假说本身所独自蕴涵，而是为一个包括这个正被讨论的假说在内的语句组所联合蕴涵。用预言这个词条中的术语来说：一个假说并不独自蕴涵观察直言句。

GOOGLE: There is one more problem that needs to be solved. Going back two paragraphs before, I mentioned the so-called necessity of mathematical truths and natural laws, but then I only discussed the necessity of natural laws. Now let us return to the question of the necessity of mathematical truths. It will be discussed using a theory of evidence known as holism. Let me first say a few words about holism. Holism was emphasized by Pierre Duhem 80 years ago. The point is that the observations we use to test a scientific hypothesis are usually not entailed by the hypothesis itself, but are jointly entailed by a group of sentences that includes the hypothesis in question. To use the terminology on PREDICTION: a hypothesis alone does not entail an observation categorical.

The bearing of this on mathematical necessity is as follows. Within the cluster of sentences needed to clinch the implication there are apt to be not only sentences from the particular science in question, physics perhaps, but also something from mathematics, and various commonsense truths that go without saying. If the predicted observation fails, the failure could in principle be accommodated by recanting anyone of the cluster. We would try to choose in such a way as to optimize future predictions, and this will have been why the particular hypothesis was fingered in the first place. The considerations that guide {142} these guesses are not well understood, but one conspicuous maxim is the maxim of minimum mutilation: disturb overall science as little as possible, other things being equal. Truths of mathematics, in particular, are pretty sure to be safeguarded under this maxim, for any revision in that quarter would reverberate throughout science.

以下是整体主义和数学必然性关系的说明。蕴涵观察结果的语句组中不仅有来自正被讨论的具体学科（比如物理学），而且很可能也有来自数学中的语句，以及各种不言而喻的常识性真理。如果被预言的观察结果没有出现，撤回语句组中的任何一个语句，原则上都可以使那个失败的预言不再能被做出。我们的选择要尽量有利于未来的预测，因此不难理解，正在讨论的具体假说会成为最先想到的候选者。我们的选择到底应该遵守哪些原则，这一点并不是很清楚的，但最小破坏原则是显而易见的：在同等条件下尽可能少地扰动科学的整体。根据这一原则，数学真理将肯定会受到特别的保护，因为对数学的修改对于整个科学来说是牵一发而动全身的。

GOOGLE: The following is an explanation of the relationship between holism and mathematical necessity. The set of statements that implies the observation will include not only statements from the specific discipline in question (such as physics), but probably also statements from mathematics, as well as various self-evident common-sense truths. If the predicted observation does not occur, withdrawing any statement in the group of statements can, in principle, prevent the failed prediction from being made. Our choices should be as favorable as possible for future predictions, so it is understandable that the specific hypothesis under discussion will be the first candidate that comes to mind. It is not very clear which principles our choices should abide by, but the maxim of minimum mutilation is obvious: disturbing the whole of science as little as possible under the same conditions. According to this principle, mathematical truths will certainly receive special protection, because revisions to mathematics have an impact on the entire science.

This accounts pretty well for the air of necessity that we attach to the truths of mathematics. Mathematics shares the empirical content of the rest of science, insofar as it contributes indispensably to the joint implying of observation categoricals; but it owes its air of necessity to our prudence in not excessively rocking the boat.

这很好地解释了我们赋予数学真理的那种必然性。数学（至少是其中那些对于蕴涵观察直言句不可或缺的部分）分享了科学其他部分的经验内容。它的必然性来自我们不愿意过度搅局的谨慎。

GOOGLE: This explains well the kind of necessity we attribute to mathematical truths. Mathematics (at least those parts of it that are indispensable for entailing observational categoricals) shares the empirical content of other parts of science. Its necessity comes from our caution in not wanting to rock the boat too much.

[1] 也即“每个等于加菲尔德的对象都出生在奥兰治”。——译者注