Armstrong’s Higher-Order Perception Theory

Philosopher David Armstrong’s higher-order perception theory proposes that a first-order mental state becomes introspectively conscious when the subject has a distinct, perception-like awareness of that state. On his materialism, both levels are neural: one brain process “scans” or represents another, producing non-inferential information about the subject’s current mind. This model helped originate contemporary inner-sense theories, but Armstrong’s changing uses of “consciousness” require qualification: the scanner clearly explains introspective awareness, yet it is disputed whether it generates phenomenal consciousness itself or merely makes an already phenomenal state available to its subject (Armstrong, 1968/1993, 1979, 1981b).

Armstrong's theory is the reflexive application of his central-state materialism (see his companion entry): consciousness in the fullest sense is the mind perceiving its own states. Distinguishing three grades of the notion—minimal consciousness (mere mental activity), perceptual consciousness (awareness of one's environment and body), and introspective consciousness (awareness of one's own current mental states)—Armstrong analyzes the third as an "inner sense," a perception-like self-scanning by which one part of the brain monitors the current states and activities of the mind (Armstrong, 1981). In other words, a first-order sensory state becomes a conscious experience, in this introspective sense, when it is scanned and thereby made the object of a higher-order representation. This makes Armstrong's the founding modern version of Higher-Order Perception (HOP), or inner-sense, theory, and, because the scanning is a physical process operating on physically realized first-order states, it extends his materialism to consciousness without invoking anything beyond the causal-role apparatus that defines mind for him in the first place (Armstrong, 1968).

Three Meanings of Consciousness

Armstrong's opening contribution is to separate questions routinely conflated in the word "conscious," distinguishing minimal, perceptual, and introspective consciousness. Minimal consciousness is the bare occurrence of mental activity—there is something mental going on, even if only a single faint sensation. Perceptual consciousness is awareness of what is currently happening in one's surroundings and body, the running sensations that guide ongoing behavior. Introspective consciousness is awareness directed inward, upon one's own perceivings, sensings, and thinkings (Armstrong, 1979). The grades are independent: a creature could have the first two without the third. By prying them apart, Armstrong reframes "the problem of consciousness" as several problems, and locates the distinctively puzzling one—reflexive self-awareness—as the target his theory is built to explain (Armstrong, 1981).

The Long-Distance Truck Driver

These distinctions reject the Cartesian idea that every mental state is transparent to its subject. Perceptions, intentions, and organized actions may occur without introspective awareness, as dramatized by Armstrong's most cited example. A long-distance truck driver, having driven for miles absorbed in thought, suddenly "comes to" and realizes he has no memory of the preceding stretch, though he steered, braked, and read the road throughout (Armstrong, 1968). He was perceptually conscious the whole time—registering and responding to his environment—yet lacked introspective consciousness, unaware of his own perceiving. The case shows that complex, purposive, environmentally sensitive behavior can proceed without reflexive awareness, and it thereby isolates introspective consciousness as something over and above mere perception. The example has become a fixture of higher-order theorizing, invoked by proponents and critics alike as the phenomenon any theory of consciousness must accommodate.

Introspection as Inner Perception

Armstrong models introspection on outer perception. Just as the senses scan the environment to produce representations of it, an inner sense scans the mind to produce representations of its current states—a self-monitoring that yields higher-order awareness of first-order episodes (Armstrong, 1981). External perception supplies information about the environment and body; inner sense supplies information about one’s current mental condition. A first-order perception, sensation, belief, or intention causes a second-order state directed toward it. This awareness need not involve words, deliberate reflection, or inference, distinguishing Armstrong’s account from later higher-order thought theories (Armstrong, 1968/1993, 1981b; Carruthers, 2026).

This inner perception has three features that distinguish it from the Cartesian picture it replaces: it is not exhaustive, since much mental activity goes unscanned; it is not infallible, since the scan can misrepresent or miss its object; and it is only contingently private, since nothing in principle forbids one brain's states being scanned by another. Consciousness, on this account, is not an intrinsic glow attaching to experiences but a relational property—being the object of a self-directed scan—that otherwise unconscious mental states acquire when monitored.

On central-state materialism, scanning is literal only at a functional level. There need be no inner spectator, Cartesian theater, or single anatomical scanner. Some neural process registers information about another neural process, as sensory systems register bodily and environmental conditions. Further awareness is possible—a monitoring state may itself be monitored—but no infinite regress follows because the higher-order state need not itself be conscious (Armstrong, 1968/1993).

Fallibility, Selectivity, and the Self

Inner perception is partial and fallible. Subjects may overlook mental states, misidentify emotions, or remain unaware of features that later evidence reveals. Armstrong therefore rejects incorrigibility, logically privileged access, and the “perfectly transparent mind.” First-person access is privileged only empirically: the brain monitors some of its own states more directly than it monitors those of other organisms (Armstrong, 1968/1993).

The apparent unity of the conscious self arises from organized monitoring within one embodied system. Armstrong distinguishes an automatic “watching brief” from deliberate introspection, in which attention is explicitly directed toward current experience. Monitoring also supports memory of mental events and coordination among psychological processes without requiring a substantial inner ego (Armstrong, 1981b).

Biological and Cognitive Function

Armstrong assigns introspection an adaptive role in purposive mental activity. Effective physical action requires continuing information about the environment so behavior can be adjusted; extended reasoning and planning similarly require information about the current stage of one’s mental activity. Calculating, deliberating, checking an intention, or revising a plan would be impossible if the system lacked access to what it had just represented or decided (Armstrong, 1968/1993).

This does not imply that all useful cognition is phenomenally conscious. Much processing remains unconscious, and minimal monitoring may suffice for coordinated thought. The proposed function enhances homeostatic control: inner sense makes selected first-order states available for correction, integration, report, and flexible guidance. As such, the theory is consistent with evolutionarily driven traits.

Higher-Order Perception versus Higher-Order Thought

Armstrong's inner-sense model pioneers the perceptual branch of the higher-order family of theories, which hold generally that a mental state is conscious in virtue of being represented by a further, higher-order state. It was developed and defended in detail by Lycan (1996), and it stands in explicit contrast to the higher-order thought account of Rosenthal (2005), on which the relevant higher-order state is a thought—a conceptual, assertive representation—rather than a percept. The dispute between perception-based and thought-based versions turns on whether inner awareness is analog and quasi-sensory or conceptual and belief-like, and on whether an inner sense requires a dedicated scanning mechanism that neuroscience still struggles to locate.

Does Higher-Order Perception Create Phenomenality?

The central question is whether Armstrong’s scanner constitutes phenomenal consciousness or only introspective consciousness or self-consciousness. Some passages identify “consciousness or experience” with awareness of one’s mental states, making the higher-order relation constitutive. Yet his later threefold classification permits minimal sensations and perceptual activity without introspective consciousness, suggesting that first-order phenomenality may precede monitoring (Armstrong, 1968/1993, 1979).

If the first-order state is already felt, the theory explains awareness of experience rather than experience itself. If it is not already felt, Armstrong must explain how a second neural representation transforms an unconscious state into one with subjective character. Other objections concern misrepresentation, apparently conscious states without accurate higher-order targets, animal and infant consciousness, and whether sub-personal monitoring can generate a unified first-person field (Carruthers, 2026; Stoljar, 2021). Armstrong’s achievement is to isolate inner awareness as a naturalizable relation, even if its connection to phenomenal feel remains unresolved.

Phenomenal Consciousness and Its Critics

For phenomenal consciousness, the theory is deflationary: the felt character of experience belongs to the first-order state, and introspective consciousness of it is a further physical monitoring, so nothing non-physical is added at either level. Two objections recur. The first is a threatened regress: if a state is conscious only when scanned, the scanning state's own consciousness seems to demand a further scan (Armstrong replies that the higher-order state need not itself be conscious). The second is that the account explains awareness of experience while presupposing the experience whose felt quality was the original puzzle, leaving qualia and the explanatory gap untouched (Armstrong & Malcolm, 1984). Whether inner-sense theory explains phenomenal consciousness or only its introspective detection remains, not surprisingly, contested (Anstey & Braddon-Mitchell, 2024).

References

Anstey, P. R., & Braddon-Mitchell, D. (Eds.). (2024). Armstrong's Materialist Theory of Mind. Oxford: Oxford University Press.

Armstrong, D. M. (1968/1993). A Materialist Theory of the Mind (revised ed.). London: Routledge.

Armstrong, D. M. (1979). Three types of consciousness. In Brain and Mind, Ciba Foundation Symposium 69 (pp. 235–253). Amsterdam: Excerpta Medica.

Armstrong, D. M. (1981b). What is consciousness? In The Nature of Mind and Other Essays (pp. 55–67). Ithaca, NY: Cornell University Press.

Armstrong, D. M., & Malcolm, N. (1984). Consciousness and Causality: A Debate on the Nature of Mind. Oxford: Blackwell.

Carruthers, P. (2026). Higher-order theories of consciousness. In E. N. Zalta and U. Nodelman (Eds.), The Stanford Encyclopedia of Philosophy. Stanford: Metaphysics Research Lab, Stanford University.

Lycan, W. G. (1996). Consciousness and Experience. Cambridge, MA: MIT Press.

Rosenthal, D. M. (2005). Consciousness and Mind. Oxford: Clarendon Press.

Stoljar, D. (2021). Armstrong’s just-so story about consciousness. In P. Anstey and D. Braddon-Mitchell (Eds.), A Materialist Theory of the Mind: 50 Years On (pp. 176–194). Oxford: Oxford University Press.