Let A denote the set of sense perceptions of a conscious being, and let B represent that conscious being's belief in the existence of an external world.

Sense perceptions include sight, hearing, touch, taste, and smell, but we can also broaden the definition to encompass any form of experiential awareness. This expansion includes the recollection of past events (memory), the sensation of time passing, emotions, cognitive processes such as reasoning and decision-making, intuitive insights, and even phenomena like hallucinations or dreams. In short, any event that can be phenomenologically experienced in consciousness.

With this understanding in mind, are reason and logical argumentation crucial in inferring B from A? If indeed they are, what mode of reasoning proves most efficacious: deductive, inductive, or abductive? For instance, can we deductively prove B from A?

Furthermore, is B the only thing that can be supported by A? Is it plausible to conceive of other potential aspects of reality, denoted as C, that might be similarly believed based on A? For example, if we were to take C to denote the spiritual realm, the supernatural, the mystical, the divine, etc.?

  • What else are those senses for, except to perceive an external world? If it were imaginary we would have no need of those organs. Commented Feb 29 at 0:23
  • 1
    Since you included all of the external world into B what is the point of C? Spiritual realm, the supernatural, the mystical, the divine, etc., are already in B, some do infer them from A. And phenomenological experiences, no matter how extended beyond sensations, are distinct from perception. They are non-propositional and cannot be the basis for inferring anything. Perception is a compound process that ends with conceptual judgments on experience and produces propositional content (that something is red, say).
    – Conifold
    Commented Feb 29 at 0:29
  • @WeatherVane That presupposes the existence of objective purpose and things being "necessary" to accomplish some goal. Those are implicit axiomatic assumptions you are adopting that need to be made explicit.
    – user66156
    Commented Feb 29 at 0:30
  • @Conifold You have a valid point, but I introduced C because I can the see the naturalist claiming that we are justified in believing in B as restricted to the natural realm, while dismissing anyone who would equally infer the existence of C as I suggested.
    – user66156
    Commented Feb 29 at 0:33
  • I can test them myself. I can click my fingers and hear the sound made, or wave my arm and see it move, taste and smell the odours from my body, and touch my nose. Commented Feb 29 at 0:37

4 Answers 4


Let A denote the set of sense perceptions of a conscious being, and let B represent that conscious being's belief in the existence of an external world.

With this understanding in mind, are reason and logical argumentation crucial in inferring B from A? If indeed they are, what mode of reasoning proves most efficacious: deductive, inductive, or abductive? For instance, can we deductively prove B from A?

Hermann von Helmholtz argues that some perceptions, such as the 3D position of objects in the 2D field of vision and the speed of objects or rate of change of position in 3D space, arise as the product of a process similar to conscious inference, but the perceptions happen automatically as the product of an unconscious process. He calls this Unconscious Inference. Based on pathological observations we consciously infer that neural structures perform the unconscious functions. But to my knowledge we don't have specific models for how the unconscious neural activity becomes the conscious qualia in our minds. Contemplating the concept of unconscious inference or perception in general further gives rise to the so-called hard problem of consciousness.

Sigmund Freud, the founder of psychoanalysis, maps the set of perceptions of a conscious being to the ego, which I define as the effort to govern action in the sensory context. Freud says the ego is weak in early life and it is dominated by two sources of cause that are both external to the ego: the id (inner drives) and reality. So, in other words, the sense perceptions of a conscious being are biologically adapted to make a distinction between efforts to govern action in the sensory context and sources of cause that are not the ego.

The ego can be viewed as a closed loop feedback system. The id and reality are open loop systems that can drive the ego from inside or aid or interfere with the ego from the outside. The newborn ego of an animal or human must inherently recognize the id and reality without having to consciously reason. Animals and young children do not demonstrate the mature human capacity for reason.

The distinction between the self and the not-self as a source of cause seems to be apriori attribute of the organism which we later incorporate into our mature conscious belief systems. Freud does not discount the subjective experience of love or the Oceanic feeling in which the boundary between the ego and the not-ego dissolves or ceases to exist in the sensory perception of the subject.

Freud describes himself as a godless Jew, and he does not describe the biological ego in terms of an I-thou relationship, except that the ego is socialized and learns to recognize other social egos in the context of reality. Others are convinced that sociality is present in the newborn organism that we recognize as mammals and other social animals. There is no logical reason why social instincts would not be inborn and arise as the product of an unconscious process based on some structures and functions of the neurons in social animals.

I note that Helmholtz is a scientist who maps mysterious sources of cause to the unconscious. That means subjective reports of God or not-God as attributes of what exist both arise as the products of an unconscious process. People who are consciously godless find arguments against the existence of God and people are conscious of the supernatural I-thou relationship need not find any arguments for God.


Firstly, you need to be clear what you mean by reasoning and argument. If you mean deliberate conscious reasoning, then the answer is 'not very much'. Most of our interactions with the world are largely automatic or subconscious and are learned behaviours. If you contemplate the question, you will find that you harbour a huge range of implicit beliefs which you have not consciously curated by subjecting them to reason. You also hold a large number of beliefs about matters that you have never experienced first-hand through your perceptions. You can believe that the Thames is shorter than the Nile, that the Arctic is colder, on average, than the Sahara, that Queen Victoria was married to Alberts, and so on endlessly-you have a huge stock of beliefs of that sort which you have probably never subjected to conscious reasoning.

You also need to consider the fact that human reasoning is far from fallible, and that a given set of sense perceptions does not lead unambiguously to a single conclusion. Which brings me to the last part of your question- clearly, yes, people can and do believe in all kinds of things that can't be justified from the evidence of their senses.


To what extent are reasoning and arguments essential to bridge the gap from sense perception to the belief in an external world?

Strictly speaking, reasoning and arguments are totally redundant. Any normal human being believes that there is an external world. More precisely, the belief is that what we perceive is the real world itself, which presumably amounts to the same thing.

The mechanic of it is really much more complex than that, but this is the basic fact. If we didn't believe that what we perceive is real, we would stay in bed in the morning and soon die of hunger.

Presumably, our sense of reality is rooted in our sensations, starting with pain, hunger and thirst. Clearly, there are more people today free of pain, hunger and thirst than ever before, and perhaps with the luxury of discussing seriously if the real world exists.


To hypothesize an external world provides the simplest explanation for our varying but regular sense perceptions.

Closing one's eyes and ears etc. changes the content of our mental conscious processes considerably.

  • 1
    How are you measuring "simplicity"? Is there a mathematical formula? Are you using Kolmogorov complexity, for example?
    – user66156
    Commented Feb 29 at 0:40
  • In the present context my measure of simplicity is Occam's razor.
    – Jo Wehler
    Commented Feb 29 at 0:42
  • "This philosophical razor advocates that when presented with competing hypotheses about the same prediction and both theories have equal explanatory power one should prefer the hypothesis that requires the fewest assumptions" - Given this definition, how are you counting the number of assumptions?
    – user66156
    Commented Feb 29 at 0:45
  • @Mark Its ironic that people who today invoke Occam, do it for the diametrically opposite intent than he did. Occam was a strict fideist in that he felt that theology and philosophy were not to be mixed up as Aquinas did. See. Also my comment on the question above
    – Rushi
    Commented Feb 29 at 4:07
  • @Mark First we need a rival theory which negates the existence of an external world, but explains the same perceptions and their dependence with the opening and closing of our eyes. Then we can study the assumptions of this theory and apply Occam’s razor.
    – Jo Wehler
    Commented Feb 29 at 7:17

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