TWO CONCEPTS OF EXTERNAL REALITY: A COMPARATIVE RESPONSE TO RADICAL SCEPTICISM

 

 

TWO CONCEPTS OF EXTERNAL REALITY: A COMPARATIVE RESPONSE TO RADICAL SCEPTICISM

Claudio Costa

 

Abstract

Radical scepticism about the external world traditionally relies on an ambiguity in the notion of “external reality.” This paper introduces a distinction between two concepts of external reality: inherent reality, grounded in empirical criteria, and adherent reality, grounded in comparative coherence between possible worlds. I argue that the sceptical and anti‑sceptical arguments both commit a fallacy of equivocation by shifting between these two senses. While inherent reality can be demonstrated, adherent reality cannot be proven; nevertheless, in the absence of any evidence for a sceptical scenario, it is rational to assume that the world possesses both forms of reality. This yields a non‑dogmatic, Wittgenstein‑compatible dissolution of Cartesian scepticism.

 

1. Introduction

The sceptical challenge concerning the external world has persisted since Descartes formulated the hypothesis of a powerful deceiver capable of generating a perfectly coherent illusion of reality. The traditional debate oscillates between two poles: the sceptic, who claims that we cannot know whether the world exists, and the anti‑sceptic, who attempts to prove that it does. Both positions presuppose that “external reality” is a single, univocal concept.

   This paper argues that the debate is misconceived. The notion of external reality is ambiguous, and the sceptical argument exploits this ambiguity. By distinguishing between inherent reality and adherent reality, we can show that both the sceptical and anti‑sceptical arguments are invalid (Costa 2014). The sceptical conclusion does not follow, and the anti‑sceptical proof is impossible. Nevertheless, a rational stance toward the external world remains available (Costa 2026).

 

2. Inherent reality : the usual sense of ‘real’

The first concept of external reality is what I call inherent reality. It corresponds to the ordinary, empirical sense in which we say that objects around us are real. This sense is grounded in criteria widely recognized in modern philosophy, from Descartes to Hume and Kant. These criteria structure our perceptual and scientific practices:

1.     Intensity: perceptual vividity, clarity, and sensory distinction.

2.     Independence: lack of voluntary control over perceptual appearances.

3.     Intersubjectivity: possibility of verification by other observers.

4.     Regularity: conformity to natural laws and contextual coherence.

When these criteria are jointly satisfied, we attribute inherent reality to the objects of perception. This is the sense in which we say that tables, trees, cities, and planets are real. It is also the sense in which scientific entities — electrons, fossils, distant galaxies — are treated as real, provided that evidence satisfying these criteria can be produced.

   Importantly, no single criterion is sufficient. Each can fail in dreams, hallucinations, illusions, or technologically induced experiences. But when all are satisfied together, the attribution of inherent reality is unavoidable.

 

3. Adherent reality: reality under comparative coherence

The sceptical challenge arises when we consider radical scenarios such as the Cartesian deceiver or the brain‑in‑a‑vat. In such scenarios, all criteria of inherent reality may be satisfied. The world of the deceived subject would appear vivid, involuntary, intersubjectively coherent, and law‑governed. It would be real‑I.

  Yet, intuitively, it would not be real in the sense that matters for the sceptic. To capture this, I introduce a second concept: adherent reality. Adherent reality is comparative. It is defined not by empirical criteria, but by the relation between two possible worlds when both become accessible. Suppose the subject escapes the deception and awakens in another world. If the new world explains the previous one as a coherent illusion — if it has greater global coherence and explanatory power — then the previous world lacks adherent reality. We see that inherent reality is empirical and phenomenological, while adherent reality is comparative and explanatory. Two worlds may be equally real‑I, but only one may be real‑A.

 

4. The sceptical and anti-sceptical arguments as equivocations

With this distinction in hand, we can reconstruct the sceptical argument:

1.     If I do not know that I am not being adherenly deceived, then I do not know that I have adherently two hands.

2.     I do not know whether I am being adherently deceived.

3.     Therefore, I do not know whether I have inherently two hands.

The conclusion shifts from reality‑A to reality‑I. This is a fallacy of equivocation.

The anti‑sceptical argument commits the same error:

1.     I know that I have inherently two hands.

2.     If I know that I have adherently two hands, then I know that I am not adherently deceived.

3.     Therefore, I know that I am not adherently deceived.

Again, the argument shifts between senses of reality. Both arguments are formally invalid. The sceptic cannot conclude that our world lacks inherent reality, and the anti‑sceptic cannot prove that it possesses adherent reality.

 

5. What can be demonstrably known and rational the assumption

The distinction yields a clear epistemological result: (1) We can demonstrate that our world is inherently real, because it satisfies the empirical criteria. (2) We cannot demonstrate that it is adherently real, because this would require comparison with another world — something we cannot perform.

This does not entail scepticism. It simply shows that the sceptical demand for proof of adherent reality is misguided.

   To address the sceptical worry, I propose the Realist Presupposition (PR):

PR: In the absence of any evidence for a sceptical scenario, we should assume that the external world is both inherently and adherently real.

PR is justified by two considerations:

(a) Russellian Parsimony

Bertrand Russell observed that the hypothesis of an external world is the simplest explanation of our experience. PR is an inference to the best explanation: it is more parsimonious to assume that the world we perceive is the only world.

(b) Wittgensteinian Framework

Wittgenstein argued that doubt is only meaningful against a background of certainty. A sceptical hypothesis requires evidence; without it, the doubt is empty. Since we have no evidence of deception, PR stands undefeated.

 

6. Conclusion

The sceptical problem concerning the external world dissolves once we distinguish between inherent and adherent reality. The sceptical argument equivocates between these senses, and the anti‑sceptical argument does the same. Inherent reality is demonstrable; adherent reality is not. Yet, in the absence of any evidence for a sceptical scenario, it is rational — and indeed necessary for meaningful doubt — to assume that the world possesses both forms of reality.

This approach avoids dogmatism, respects the limits of justification, and aligns with both Russell’s inferential pragmatism and Wittgenstein’s hinge epistemology. It offers a clear, non‑foundationalist, non‑metaphysical dissolution of radical scepticism.

 

References:

Costa, Claudio (2014). Lines of Thought: Rethinking Philosophical Assumptions. (Cambridge Scholars Publishing), Chapter Six.

Costa, Claudio (2026). Introdução histórica à filosofia (Europa Books), cap. V (to be published).