Introduction
Welcome to our next lesson. In our previous sessions, we explored the philosophical foundations of intuitionism. We started with Brouwer's constructivist philosophy, which led to the rejection of the Law of the Excluded Middle. We then examined the Brouwer-Heyting-Kolmogorov (BHK) interpretation, a systematic, alternative semantics for logic where the meaning of connectives is defined not by abstract truth-conditions, but by concrete proof-conditions.
Today, we delve deeper into the philosophical programme of Michael Dummett, who sought to provide a general argument for this shift in perspective. Dummett believed that debates in metaphysics—such as realism versus anti-realism—and even debates about the correct logic could be settled by first getting clear on the nature of meaning.
Your learning outcome for this lesson is to analyse Dummett's argument that a theory of meaning must be grounded in the public manifestation of understanding. This is famously known as the Manifestation Argument. We will see how this argument challenges the classical, realist picture of meaning and truth, thereby preparing the ground for an anti-realist alternative like intuitionism.
1. Dummett's Project: From "Meaning is Use" to a Theory of Meaning
At the heart of Dummett's philosophy is an idea he inherits from the later work of Ludwig Wittgenstein: the slogan that the meaning of a word is its use in the language.
Dummett, Michael | Internet Encyclopedia of Philosophy
The Internet Encyclopedia of Philosophy provides a concise introduction to how Dummett adopted Wittgenstein's central idea. This will set the stage for our analysis.
Please read the short section '2.a. Wittgenstein: Meaning as Use'. Focus on the core idea: if to know the meaning of a word is to be able to use it correctly, then a theory of meaning must be an explanation of this practical ability.
If meaning is use, then to understand a language is not to be in some private mental state, but to possess a practical, demonstrable skill. A theory of meaning, for Dummett, should therefore be a theoretical representation of what this practical knowledge consists in.
Dummett argues that the classical, Fregean-inspired theory of meaning—which identifies understanding a sentence with knowing its truth-conditions—is a powerful model, but it comes with a significant philosophical assumption: realism. Realism is the view that statements are made true or false by a reality that is independent of our minds and our ability to know it. This implies that the truth-condition of a sentence might be verification-transcendent—that is, it might be a condition that we are, even in principle, incapable of recognizing or verifying.
Dummett challenges this. He argues that a theory of meaning should not be based on abstract, potentially unknowable truth-conditions. Instead, it must be grounded in something we can actually learn and display: our ability to use language.
Michael Dummett on Frege, Truth, Meaning & Realism (1997)
In this clip from a 1997 interview, Dummett clearly articulates his alternative vision for a theory of meaning.
Please watch the segment from 20:58 to 24:55. Notice how Dummett contrasts the classical view ('to understand a sentence is to know what has to be the case for it to be true') with his own, which is based on what 'counts as establishing a sentence as true'. This is a crucial distinction.
Dummett's proposal is to replace the realist's notion of a truth-condition with the anti-realist's notion of a justification-condition or proof-condition. The central concept in a theory of meaning should be what we can recognize as justifying an assertion. This ties meaning directly to our epistemic and linguistic practices.
2. The Manifestation Constraint
This leads us to the core principle of today's lesson. If understanding is a practical ability, then it must be publicly observable. An individual's knowledge of the meaning of an expression must be capable of being manifested in their use of that expression. This is the Manifestation Constraint.
This idea has deep roots in the history of analytic philosophy. It can be seen as a logical consequence of Frege's rejection of psychologism. For Frege, senses (meanings) had to be objective and publicly shareable to explain how communication is possible. If meaning were a private mental image (as in Locke's theory), we could never be sure we meant the same thing.
[PDF] 31 Michael Dummett (1925– )
The following text traces the intellectual heritage of the manifestation constraint, from Frege's insistence on the objectivity of sense to Wittgenstein's focus on use.
Please read the section titled 'Frege and Wittgenstein on the objectivity of sense' (pp. 381-384). Focus on how the need for meaning to be communicable and public leads to the conclusion that 'grasp of its sense has to be construed in terms of possession of an ability to use it in certain public and observable circumstances.'
To summarize the key move:
- Meaning must be public and communicable (Frege's anti-psychologism).
- Therefore, what it is to know the meaning of an expression cannot be a private, inner state.
- Rather, knowledge of meaning must consist in a practical ability to use the expression correctly according to public norms.
- Crucially, this ability must be something that can be publicly manifested. If there were an aspect of your understanding that you could never, even in principle, display in your linguistic behaviour, it could play no role in public communication and thus could not be part of meaning.
This is the manifestation constraint. It's not yet an argument, but a condition that any plausible theory of meaning must satisfy.
3. The Manifestation Argument against Realism
Dummett weaponizes the manifestation constraint to launch a direct attack on semantic realism. The argument takes the form of a reductio ad absurdum.
[PDF] 31 Michael Dummett (1925– )
The same document you just read lays out the manifestation argument with formal precision. We will work through its steps.
Please read the section 'Dummett’s manifestation argument' (pp. 386-387). The text formalizes the argument into eight steps. As you read, focus on identifying the role of each premise, especially the crucial steps (4), (5), and (6).
Let's reconstruct the argument's logic, focusing on a class of statements that might have verification-transcendent truth-conditions (e.g., Goldbach's Conjecture, or a statement about the distant past like "Julius Caesar sneezed at noon on his 30th birthday").
- Assume for reductio: Realism is correct. The meaning of these statements is given by their verification-transcendent truth-conditions.
- From the definition of understanding: To understand these statements is to know their verification-transcendent truth-conditions.
- Apply the Manifestation Constraint: This knowledge must be fully manifestable in the speaker's use of the language.
- The Challenge: What linguistic practice could possibly manifest knowledge of a condition that, by definition, transcends all possible evidence?
- A speaker can certainly show their ability to use the sentence: they can appraise evidence for or against it, recognize some of its logical consequences, use it in questions, etc.
- But, Dummett argues, all of these manifestable abilities can be fully explained by crediting the speaker with an understanding of what counts as evidence or proof for the statement.
- The Crucial Premise: There is no observable behaviour that distinguishes a speaker who grasps the verificationist meaning from a speaker who supposedly grasps the realist's verification-transcendent meaning. The supposed extra knowledge of the realist is an "idle wheel"; it does no explanatory work. Since this knowledge can never be manifested, it cannot be what understanding consists in.
- Contradiction: Our assumption (1) implies that understanding consists in knowledge that cannot be manifested (5), which contradicts the manifestation constraint (3).
- Conclusion: Therefore, the initial assumption must be false. We must reject realism and the idea that meaning is given by verification-transcendent truth-conditions.
The upshot is that a theory of meaning must be built on a foundation that is epistemically constrained—based on what we can know, prove, or verify. This provides a powerful, general argument for adopting a semantics like the BHK interpretation we studied in the last lesson.
4. A Clash of Philosophies: Dummett vs. Davidson
To see the manifestation argument in action, it is illuminating to watch Dummett in conversation with Donald Davidson, another of the 20th century's most important philosophers of language. Davidson advocated for a sophisticated truth-conditional theory of meaning. In this debate, you can see Dummett press his core challenge.
Donald Davidson and Michael Dummett - Language and Philosophy
This video captures a fascinating debate between Michael Dummett and Donald Davidson. We will watch two key moments that highlight Dummett's position.
Please watch the following two clips: 02:20 - 04:54: Dummett lays out his initial criticism. He argues that traditional theories of truth assume meaning is understood, whereas Davidson's theory of meaning assumes truth is understood. Dummett insists that 'truth and meaning are concepts that have to be explained together.' 29:59 - 34:25: Dummett argues that the notion of being right or wrong in what one says is inextricably linked to the public practice of 'giving reasons for' and 'challenging' assertions. This is a prime example of a manifestable linguistic practice that, for Dummett, is central to meaning. \nAs you watch, consider how Dummett is constantly trying to ground the theory of meaning in what speakers actually do.
In the first clip, Dummett's charge that Davidson "tak[es] truth as already understood" is a direct consequence of the manifestation argument. A theory of meaning should explain our grasp of concepts like truth by grounding them in our public practices. It cannot simply assume them as primitive, because that would leave unexplained how we manifest our grasp of such a concept.
In the second clip, the focus on the practice of giving and asking for reasons is a concrete example of what a manifestation-based theory of meaning would look like. It is through these public, rule-governed activities that we learn, display, and enforce the meanings of our words.
Conclusion
Today we have dissected one of the most influential arguments in contemporary philosophy of language. Dummett's demand that understanding be manifestable in use provides a powerful lever for moving from a realist to an anti-realist conception of meaning.
Key Takeaways:
- Meaning as Use: Following Wittgenstein, Dummett argues that a theory of meaning must explain the practical ability to use a language.
- The Manifestation Constraint: Knowledge of meaning must be publicly manifestable in a speaker's linguistic behaviour. Any supposed aspect of understanding that is, in principle, un-manifestable is not a genuine part of meaning.
- The Manifestation Argument: This is a reductio argument against semantic realism. It claims that knowledge of verification-transcendent truth-conditions (the cornerstone of realism) cannot be manifested. Therefore, realism provides a defective account of what linguistic understanding consists in.
- The Anti-Realist Alternative: The argument pushes us towards an anti-realist theory of meaning, where meaning is explained in terms of epistemically constrained concepts like proof, verification, or justification—precisely the kind of semantics offered by the BHK interpretation.
Preview of the Next Lesson:
We have now analysed the manifestation argument itself. In our next lesson, we will complete this module by exploring its direct consequences for logic. The learning outcome will be to evaluate how Dummett's 'manifestation argument' provides a justification for intuitionistic logic over classical logic. We will see how accepting this argument can lead one to conclude that classical logic, for certain areas of discourse, is not merely questionable, but philosophically unsound.