Projected Synopsis and Chapter Details
After reviewing the current research state of the issue of incommensurability and
clarifying many facets and ramifications of the notion of incommensurability in chapter
1, I focus on the accepted interpretation, namely, the translation-failure interpretation in
chapter 2. According to this interpretation, to say that two scientific theories are
incommensurable is to say that the languages employed by the theories are not mutually
translatable and therefore successful communication between them breaks down. The
failure of mutual translation is caused by the absence of meaning-referential continuity
due to the radical variance of meaning and/or reference of the terms employed by the
languages. The interpretation has dominated the discussion of the issue of incommensurability for the past four decades. With focus on the meaning-referential relation
between two scientific languages, the notions of meaning, reference, and translation have
been subjected to many historically erudite and conceptually fine-grained analyses.
However, until now no significant progress has been made to clarify the notion of
incommensurability. We still even do not know what incommensurability is. The main
reason responsible for such slow progress, in my judgment, is that the translation-failure
interpretation is on a wrong track. It cannot establish a tenable and integrated notion of
incommensurability. Reference to the notion of translation neither identifies nor resolves
the problem of incommensurability. Therefore, the translation-failure interpretation has
to be given up.
The furor over the translation-failure interpretation has obscured the most
interesting aspect of incommensurability, namely, the obstruction of the truth-value
functional relation between incommensurable scientific languages. I propose to switch
our attention from the meaning-referential relation to the truth-value functional relation
between rival scientific languages. It is the truth-value functional relation, instead of the
meaning-referential relation, that is the dominant semantic relation in the case of
incommensurability. By identifying and clarifying the obstruction of the truth-value
functional relation between two rival scientific languages, I intend to present and defend
the presuppositional interpretation of incommensurability throughout the rest of the
book.
Taking such a new perspective, I puzzled over late Kuhn’s mature works on
incommensurability. To my surprise, I found that Kuhn has already hinted at this new
direction in many profound ways. Unfortunately, these Kuhnian insights are ignored by
the current literature (and are likely ignored by Kuhn himself). I argue in chapter 3 that
Kuhn's alleged taxonomic interpretation of incommensurability is grounded on an illdefined notion of untranslatability and is hence radically incomplete. To supplement it, I
give a different reading of Kuhnian taxonomic incommensurability based on a
combination of a logical-semantic theory of taxonomy, a semantic theory of truth-value,
and a semantic theory of cross-language communication. According to my
reconstruction, two scientific languages are incommensurable when core sentences of one
language, which have truth-values when considered within its own context, lack truthvalues when considered within the context of the other due to the unmatchable taxonomic
structures underlying them.
My dissatisfaction with the translation-failure interpretation is not only caused by the
many theoretical difficulties it faces, but also due to my observation that it is unable to
elucidate many classical confrontations between seemingly incommensurable scientific
theories. These familiar conceptual confrontations are not confrontations between two
scientific languages with different distribution of truth-values over their assertions, but
rather confrontations between two languages with different distribution of truth-value
status over their sentences due to incompatible fundamental assumptions presupposed by
the languages. Consequently, a communication breakdown between two language
communities is not signified by the untranslatability, but rather indicated by the
occurrence of a truth-value gap between them. To illustrate this intuition, I present two
case studies in chapter 4: one is the Newton-Leibniz debate on the absoluteness of space.
The other is contemporary Western medical theory versus traditional Chinese medical
theory.
According to the notions of semantic presupposition and truthvaluelessness
presented and defended in chapter 5, a sentence (say, "The present king of France is
bald.") would be truthvalueless if one of its semantic presuppositions (say, "The present
king of France exists.") failed. It is imaginable that if there were one semantic
presupposition underlying numerous sentences of a scientific language (say, the existence
of phlogiston in phlogiston theory), then the occurrence of truthvalueless sentences due to
the failure of the shared semantic presupposition would not be restricted to a few
individual sentences, but rather spread to the whole language and result in numerous
truthvalueless sentences in the language. I introduce, in chapter 6, a notion of
presuppositional language to explain the possible occurrence of numerous truthvalueless
sentences. I start with an important, but often ignored distinction between the notions of
truth-value and truth-value-status (whether a well-formed, meaningful sentence is a
candidate for truth-or-falsity), and, correspondingly, the distinction between truth conditions and truth-value conditions. The current discussion of incommensurability and its
related topics – such as conceptual schemes, translation, and theory comparison – are
based on a tacit assumption that every sentence in a scientific language has a determinate
truth-value. What makes two scientific theories incommensurable, on the traditional
view, is the redistribution of truth-values over their assertions. On the contrary, I argue
that what should concern us, in the discussion of incommensurability and related issues,
is not truths or truth-values of assertions, but rather the truth-value-status of the sentences
used to make the assertions.
On the basis of the formulation of semantic presupposition set up in chapter 5, I
propose the truth-value conditions of a sentence (Convention P): a sentence is true-orfalse, when considered within a scientific language, if and only if its (sufficient) semantic
presupposition is held to be true in the language. Truth-value status is thus relative to a
specific scientific language. It is a scientific language that creates the possibility of truthor-falsehood. Therefore, it is possible for one sentence to be the candidate for truth-orfalsity in one scientific language and is assertable, but not in the other.
Most scientific languages are presuppositional languages. By a presuppositional
language I mean an interpreted language whose core sentences presuppose one or more
fundamental shared semantic presuppositions. When two such languages conflict with
one another, it is likely that many sentences of one language, when considered within the
context of the other, are truthvalueless due to the failure of one of the shared semantic
presuppositions. This explains the occurrence of numerous truthvalueless sentences we
have observed. In this case we say that a truth-value gap occurs between the two
languages.
The hallmark of a presuppositional language is its metaphysical commitments. In
chapter 7, I identify and illustrate three kinds of metaphysical commitments: existential
suppositions about the existing entities in the world around a language community (say,
phlogiston); universal principles about the existent state of the world surrounding the
community (say, the postulate of absolute space); categorical frameworks about the
structure of the world around it (say, the taxonomy of Copernican astronomy). These
factual commitments are nothing but some fundamental shared semantic presuppositions
of a scientific language. They determine the truth-value status of sentences in a language.
Mutual violation or suspension of each other's metaphysical commitments would result in
a truth-value gap between two presuppositional languages.
Incommensurability is a semantic notion closely related to the problem of how
two scientific language communities can successfully communicate with each other. We
find that two incommensurable language communities often experience a communication
breakdown. To explain this so-called phenomenon of incommensurability, I present, in
chapter 8, a truth-value conditional account of understanding to spell out an essential
necessary condition of effective cross-language understanding. I argue that for one to
effectively understand a sentence of an alien language is not just to simply make sense of
it. One has to comprehend the point of what is being said or what is being presented /
argued for. For one to comprehend the point of saying, one has to grasp the metaphysical
commitments presupposed by the language. Therefore, to grasp the metaphysical
commitments of an alien language is necessary to understand it effectively. I conclude
that the notion of truth-value status plays an essential role in effective understanding: an
interpreter can effectively understand an alien language only if the sentences of the
language, when considered within the context of the interpreter's language, are
(conceptually) true-or-false. The fact that numerous sentences of an alien language, when
considered within the context of the interpreter's language, lack (conceptually possible)
truth-values indicates semantically that he/she cannot understand it effectively. In this
case, the would-be communicators will experience a complete communication
breakdown.
It would be a mistake to assert that the would-be-communicators of two
incommensurable languages cannot understand one another per se. Anything that can be
said in one language can be understood, with imagination and effort, by the speaker of
another language through language learning. The communication breakdown only
signifies that the process of understanding is not closed but still open. After rejecting
both the absolutistic-projective way and the relativistic-adoptive way of understanding, I
propose to follow the hermeneutic approach to understanding, outlined by Heidegger and
Gadamer, to resolve the problem of mutual understanding between the speakers of two
incommensurable languages.
However, although hermeneutic understanding can overcome complete
communication breakdowns due to the failure of effective understanding, there still exist
some much more significant cases of communication breakdowns between two
competing languages with incompatible metaphysical commitments. Understanding
should be distinguished from linguistic communication. Understanding is necessary, but
not sufficient for successful communication between two incommensurable languages.
In many cases, although the speakers of two incommensurable languages can understand
each other’s language very well, they cannot communicate successfully with the other
side if the metaphysical commitments of the two languages are incompatible. This is
because successful communication between two language communities requires
compatible metaphysical commitments. When the metaphysical commitments of two
competing languages are incompatible, the communication between them is inevitably
partial. In this case, the speakers of two competing languages can understand but cannot
successfully communicate with one another. They experience a partial communication
breakdown. I argue that such a partial communication breakdown is inevitable between
two competing languages with incompatible metaphysical commitments. It is the
existence of such partial communication breakdowns, i.e., communication breakdowns
per se, that establishes that the phenomenon of incommensurability is metaphysically
significant.
A communication breakdown between two language communities is semantically
indicated by the occurrence of a truth-value gap between them. The communication
breakdown due to the occurrence of a truth-value gap signifies that the languages are
incommensurable. As a matter of fact, a truth-value gap between two competing
languages L(T1) and L(T2) due to incompatible metaphysical commitments plays a
double role in the incommensurability relation between them. On the one hand, the
occurrence of a truth-value gap between L(T1) and L(T2) indicates, at the semantic level,
a communication breakdown between the two language communities. On the other hand,
such a gap is caused by, and can be used to indicate semantically, an ontological
incompatibility between L(T1) and L(T2) at the ontological level (as I will show shortly).
Therefore, I think that it is much more appropriate to use the occurrence of a truth-value
gap caused by incompatible metaphysical commitments, signified by communication
breakdowns, as a touchstone of incommensurability. By definition, two scientific
languages are incommensurable (in a broad sense) when core sentences of one language,
which have truth-values when considered within its own context, lack (either actual or
conceptually possible) truth-values when considered within the context of the other. The
occurrence of a truth-value gap between the two languages indicates the communication
between the two language communities is problematic and inevitably partial.
More precisely, corresponding to two degrees of communication breakdowns (partial
and complete communication breakdowns), we can identify two degrees of
incommensurability: moderate vs. radical incommensurability. The moderate
incommensurability relation between two competing languages, associated with a partial
communication, is the incommensurability of real metaphysical significance. In contrast,
the radical incommensurability relation between two competing languages, associated
with a complete communication breakdown, can be overcome in principle. The above is
what I argued at length in chapter 9.
Questions remain after the identification of the real conceptual source of
incommensurability: What is the ontological status of metaphysical commitments? What
is the ontological consequence when two theories are incommensurable? These are the
issues to be addressed in chapter 10. According to my contextual factualist account of
intentionality, a possible fact is a state of affairs specified by a sentence with a (actual)
truth-value. I argue further that all the possible facts associated with a scientific language
constitute the ontology of the language. Here I make use of a modified Wittgensteinian
notion of fact-ontology with Quine's style. According to this notion of ontology, the
question, “What is the ontology of a scientific language?” should be construed as the
question, “What possible facts, according to a given language, exist in the world under
consideration?” Since it is the metaphysical commitments of a language that determine
the truth-value status of the sentences under consideration, it is the metaphysical
commitments that determine whether the states of affairs expressed by these sentences
are possible facts. The function of metaphysical commitments of a scientific language is
thus to indicate what counts as possible facts from the point of view of the believers of
the language. Therefore, the metaphysical commitments of a scientific language are
actually its ontological commitments, which determine what counts as alleged possible
facts for the language, and whether the language is fit to describe the world around the
language community.
Since the essence of a scientific language is represented by its metaphysical
commitments, two languages differ in just this regard, namely, by being laden with
different types of metaphysical commitments. Thus the ontological relationships
between two scientific languages can be reduced to two kinds of relationships between
metaphysical commitments embodied in the languages. Imagine that two
presuppositional languages L(T1) and L(T2) embodied with incompatible metaphysical
commitments confront one another. These two ontologically incompatible languages,
due to mutual exclusion of each other's metaphysical commitments, will disagree on the
domains of possible facts associated with the other language. Whether a state of affairs
counts as a possible fact in one language is indicated by whether the sentence used to
describe the state of affairs has a (actual) truth-value when considered within the context
of the language. Hence, disagreement between L(T1) and L(T2) on the domains of
possible facts recognized by the other would manifest itself as the disagreement on truthvalue status of core sentences used to describe the possible facts in the other language.
Consequently, a (actual) truth-value gap occurs between the two languages. The
occurrence of a (actual) truth-value gap between L(T1) and L(T2) leads to a linguistic
communication breakdown per se between the two language communities. This kind of
communication breakdown due to the occurrence of a (actual) truth-value gap signifies
that L(T1) and L(T2) are incommensurable in principle. This is the real secret of
incommensurability.
At last, I point out, in chapter 11, that my interpretation has at least three
advantages over the standard interpretation: (a) it establishes the integrity and tenability
of the notion of incommensurability. (b) It confirms the existence of the incommensurables and makes them a metaphysically and epistemologically significant phenomenon.
(c) It incorporates the merits of the standard interpretation into its framework and avoids
its weakness. Specifically, I argue that my interpretation renders rational theory
comparison possible based on the presuppositional incompatibility relation between two
incommensurable languages.