Multiple Realizability 多重具現性

The multiple realizability thesis about the mental is that a given psychological kind (like pain) can be realized by many distinct physical kinds: brain states in the case of earthly mammals, electronic states in the case of properly programmed digital computers, green slime states in the case of extraterrestrials, and so on.
多重具現性，指的是心理狀態（例如疼痛）可以由不同的物理性質來說明。例如大腦神經狀態，不同的路生哺乳類、由設計程式來計算的電腦、長得像綠色黏漿的外星人，只要有腦神經狀態，不論他是甚麼東西，都能由多重具現性來說明。
Correctly characterizing the realization relation remains a contentious(debatable) matter in analytic metaphysics (Gillett 2003, Polger 2004). But whatever the correct account turns out to be, the multiple realizability thesis about the mental is that a given psychological kind (like pain) can stand in that relationship to many distinct physical kinds.
In a pair of examples illustrating multiple realizability in special sciences (economics and psychology), Jerry Fodor (1974) implicitly distinguished between two types of the relation.
Call the first type, illustrated in the examples provided at the end of the previous paragraph, multiple realizability "over physical structure-types": creatures with distinct physical structures realizing their psychological states can nevertheless entertain the same psychological states. A more radical type of multiple realizability would obtain if a token physical (e.g., nervous) system can realize a single mental kind via distinct physical states of that same system at different times.
Call this second sense multiple realizability "in a token system over times." (These terms are from John Bickle 1998, Chapter 4.) This second sense is more radical because there could be a disjunction of physical states realizing each mental kind for every existing cognizer. The importance of the more radical type is discussed further.

In a series of papers published throughout the 1960s, Hilary Putnam into the introduced multiple realizability into the philosophy of mind. Against the "brain state theorists," who held that every mental kind is identical to some as-yet-undiscovered neural kind, Putnam (1967) notes the wide variety of terrestrial creatures seemingly capable of experiencing pain. Humans, other primates, other mammals, birds, reptiles, amphibians, and even mollusks (e.g., octopi) seem reasonable candidates. But then for the “brain state theory” to be true, there must be some physical-chemical kind common to this wide variety of pain-bearing species, and correlated exactly with each occurrence of the mental kind. (This is a necessary condition of the hypothesized type-identity.) But comparative neuroanatomy and physiology, facts about convergent evolution, and the corticalization（皮質層化） of function (especially sensory function) as cortical mass increases across species all speak against this requirement.
一九六零年代，帕南展開在心靈哲學當中對多重具現性的探究。他認為大腦狀態的理論所主張的，心理狀態與某些還不很清楚地被我們知道的類神經狀態是可等同的，像陸地生物和人類的疼痛可藉由大腦狀態說明。如果大腦狀態的理論是對的，物理和化學的那些性質就能用來說明疼痛這種心理狀態的發生，但是，相對的，神經解剖學和生理學研究的進路是研究大腦皮質層功能的學科，他們對於這種等同的主張還是抱持著質疑的立場。
In addition, early mind-brain identity theorists insisted that these identities, while contingent, hold by virtue of natural (scientific) law. But then any physically possible cognizer (e.g., pain-bearer) must also be capable of possessing that physical-chemical kind. Here the well-known philosophers' fantasies enter the discussion. Silicon-based androids（矽基人造人）, artificially intelligent electronic robots, and Martians with green slime pulsating（外星人） within their skulls all seem to be possible pain realizers. But they lack “brain states” comparable to ours at any level of physical description. Further still, these mind-brain identity theories were supposed to be completely general. Every mental kind was held to be identical to some neural kind. So the critic needs to find only one mental kind, shared across species yet realized differently at the physical-chemical level. Putnam acknowledges that the early identity theories were empirical hypotheses. But one of their consequences was "certainly ambitious" and very probably false.
而且，心腦同一論與等同理論的主張還是仰賴對於自然律的偶然性。（“自然律“幾乎是科學哲學研究中的濫觴。）而這些自然律的偶然性僅只是科學實驗過程當中可能的而已。無論是人造人還是人工智慧的機器人，或者是外星人腦殻的大腦狀態，它們的疼痛與我們人類的疼痛也只是具現上可能的（realizational possible)而已。具現上可能並不是必然的關係。也就是說 ，無論非人類的東西的疼痛與人累的疼痛有多像，都只是物理性質上相容罷了。心腦同一論的主張基本上是一個太強的主張，任何心裡狀態都能與大腦狀態等同，是必然的嗎？如果這是一個必然的關係，任何一個心理狀態都不能被除了它以外的物理性質所具現。帕南認為，早期的等同理論只能是經驗上的實驗的假設，最後還是必須面對“確定性的歧義“的挑戰，但是這個理論（心腦同一論）的主張很有可能最後還是錯誤的。
Stated in canonical form（語法或結構的最基本形式）, Putnam's original multiple realizability argument draws an anti-identity theory conclusion from two premises:

1. (the multiple realizability thesis) All mental kinds are multiply realizable by distinct physical kinds.
2. If a given mental kind is multiply realizable by distinct physical kinds, then it cannot be identical to any specific physical kind.
3. (the anti-identity thesis conclusion) No mental kind is identical to any specific physical kind.

1.所有的心理狀態都可以由物理性質所具現。（根據心理狀態與物理性質之間的多重具現關係）

2.如果心理狀態是可以由各種不同的物理性質所多重具現的，那麼單一個心理狀態就不可能和其他類的物理性質所等同。（根據1, 存在量化號的否定用QN展開為全稱量化後個體的否定）

3.（反等同論的結論）沒有任何心理狀態是與任何物理性質等同的。（根據1, 2，MP )

In this simple form, this is a deductively valid argument.
Fodor (1974) extended Putnam's initial argument by arguing that reductionism imposes too strong a constraint on acceptable theories in special sciences like psychology. According to Fodor, reductionism is the conjunction of "token physicalism" with the claim that there are natural kind predicates in an ideally completed physics corresponding to each natural kind term in any ideally completed special science. He characterized "token physicalism" in turn as the claim that all events that science talks about are physical events—a weaker thesis than reductionism or type-type physicalism. Consider the following string of numerals:

1 1 2.

This string contains two types of numerals (1 and 2), but three tokens of the two types (two tokens of the numeral type 1 and one token of the numeral type 2). Mental states admit of a similar ambiguity. When you and I both entertain the belief that Fodor advocates a Language of Thought, one type of mental state is entertained, but two tokens of that type (your belief state and my belief state). Type-type physicalism insists that types of mental states are identical to types of physical states; this view runs afoul of multiple realizability. But token physicalism only insists that each token occurrence of each type of mental state is identical to some token occurrence of a physical state type—not necessarily an occurrence of a token of the same physical state type on each occasion.
Fodor根據帕南論證的基本想法，主張化約論的做法就像心理學一樣，太過於強調科學實驗的相容性，但是忽略心理狀態與科學實驗語彙的歧義性。如果你接受Fodor的思維語言假設（language of thought hypothesis)，單一心理狀態類型可以有兩種個例，比如我和妹妹都相信今天母親生日，我和妹妹都有“相信“這個心理狀態，但是我和妹妹的心理狀態都只是“相信“這個心裡狀態的個例。類型物理論認為心理狀態的類型與物理狀態類型是等同的，這個觀點造成多重可具現性的淒慘下場。但個例物理論只認為心理狀態顯示了那個類型的心理狀態，和心理狀態並不是等同的。
Fodor gave reductionists the best-developed theory of reduction at the time: Ernest Nagel's (1961) "derivability" account of intertheoretic reduction. Nagel's account "connects" disparate(different) elements of the reduced and reducing theories' vocabularies via "bridge laws" (not Nagel's term!) and claims a reduction when the laws of the reduced theory are derived from the laws of the reducing and the bridge laws. According to Fodor (1974), if reductionism is to establish physicalism, these cross-theoretic bridge laws must assert (contingent) identities of reduced and reducing kinds. But given multiple realizability, the only way this can obtain is if the physical science constituent of a psychophysical bridge law is a disjunction of all the terms denoting possible physical realizations of the mental kind. Given the extent and variety of actual (not to say possible) physical realizations, it is overwhelmingly likely that the disjunctive component will not be a kind-predicate of any specific physical science. It is also overwhelmingly likely that the disjunctive component will not appear in any genuine law of a specific physical science. Multiple realizability thus demonstrates that the additional requirement of reductionism (beyond token physicalism) is empirically untenable.
Fodor的化約主張正是Nagel跨理論化約之意：可推導性。Nagel認為，“連結“、化約到物理性、化約理論的語彙通道：自然律之橋；也就是說，當我們進行化約時，理論所提供的化約線索是可以藉由化約的規律所推導進行的。Fodor認為，如果物理論的化約論是可行的，那麼跨理論的自然律之橋就顯示，藉著偶然上的等同關係，我們的化約工作可以進行：心理狀態化約到物理性。但，多重可具現性只能說，如果物理科學建構了心理學自然律，我們也只能說，心理狀態化約到物理的辭彙是物理上具現可能的。因為多重可具現性所主張的現實上物理性只是和我們的實驗語彙可相容，不代表它已經克服了物理科學實驗的必然連結性，甚至已經可以等同於我們的物理世界所呈的所有科學實驗結果。多重可具現性因此只抓住了化約論（除了個例物理論）所加上的經驗判斷，但是經驗判斷仍然令得我們存有困惑。