A vast variety of experiences can be occasioned by psychedelic substances, from the mundane or irritating, to the sublime, world-destroying, world-creating. Under the influence we seemingly encounter alien states of mind, and alien worlds – the mysterious subjective and the mystery of the objective: can psychedelic states reveal any objective reality or are they always subjective? For some explorers, there is a 'noetic' aspect to certain psychedelic states: a feeling that one has undergone, as William James puts it, 'states of insight into depths of truth unplumbed by the discursive intellect. They are illuminations, revelations'. The feeling of obtaining novel knowledge concerning fundamental reality is often accompanied by correlated qualms. In the words of Nobel laureate Octavio Paz, 'The person who takes a [psychedelic] drug implicitly doubts the solidity of reality – he is not sure that it is what it appears to be and what our instruments define it as being, or he suspects that another reality exists.'

For some psychonauts, such noetic feeling suffices for full-on belief in the objective existence (the veridicality) of the apparent realities perceived. Such apparent realities may involve fearful four-dimensional praying mantis machines, fiendish pixies pursuing some vital interstellar factory logistics, or one's becoming a sentient polyhedron, eternally spinning for the sake of love. William James, however, reserves noeticism more for the grander metaphysical schemes such as belief in the unreality of time or space, the unity of subject and its object, moreover the ultimate unity of all things, the ubiquity of minds in all entities or mind in all entities (panpsychism and pantheism, respectively), and an intuition of intrinsic values embedded within nature.

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"Under the influence we seemingly encounter alien states of mind, and alien worlds – the mysterious subjective and the mystery of the objective."

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For others, such so-called psychedelically induced mysticism yields no insight into reality at all. Such rejection comes in two main, albeit contrary, strands: the theist and the physicalist. Certain theistic thinkers consider induced mysticism to be, as it were, fake mysticism, revealing no truth in comparison to the revelations of the ordained saints and established mystics. On the other side, the physicalist, or materialist, also takes induced mysticism to be non-revelatory and thus merely subjective. That which the physicalist and the theistic, religious sceptic share is the belief that the existence of a physical substance (the drug) and its neurological ramifications (the neural correlates of psychedelic consciousness) is a sufficient condition for explaining the psychedelic experience. Here there is no need to involve the divine or the metaphysical as a cause of a psychedelic experience. Thus the experience is either dismissed as sacrilegious and delusional, or as merely delusional.

But beyond these two extremes – the all-out belief of the mantis-veridicalists and the all-out rejection of the theist-physicalists – there lies the possibility that certain experiences are veridical, others non-veridical: some revelations, others hallucinations. How could this veridicality be determined?

For a veridical experience one requires: 1. physiological perceptive processes, such as functioning eyes and brain, 2. an external perceived object, such as a lamp. Both 1. and 2. (subject and object) are necessary for an experience of the real. Neither is sufficient, i.e. enough, by itself to yield a real, veridical experience. 1. without 2. would be a hallucination; 2. without 1. would not be an experience at all. We see, therefore, that the criterion for determining an experience as hallucinatory is not merely the existence of neural correlates of the experience – we must also rule out the existence of that which is perceived. Consequently, merely presenting the neural correlates of psychedelic experience does not imply that the experience is non-veridical, hallucinatory. In likewise fashion, presenting the neural correlates of a perceived lamp does not imply that the lamp is a hallucination. Neural correlates of psychedelic consciousness neither prove nor disprove that which is experienced – they are not a sufficient condition for establishing non-veridicality. Neural correlates would be expected for both veridical and non-veridical psychedelic experience.

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"Merely presenting the neural correlates of psychedelic experience does not imply that the experience is non-veridical, hallucinatory."

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How, then, could we rule out the existence of the external perceived object of a psychedelic experience, as neural correlation alone cannot offer this? There are a number of criteria that generally determine whether what we experience is real or not. These include:

• Sensibility: Something sensed by the traditional five senses (sight, sound, etc.) is commonly taken as veridical. Sensibility is useful but not sufficient to give us knowledge of what exists. There are things that exist of which we can be cognizant that are not perceived through the traditional senses, such as mathematical theorems and logical axioms. More pertinently, we cannot even directly perceive the consciousness of others through these senses. Thus we cannot rule out the existence of objects of psychedelic experiences solely on the basis that they cannot be observed through the traditional senses.
• Shared objects of experience: If only I see the lamp, but others do not, I may question the veridicality of my experience. But the experiences of grander psychedelic phenomena listed above – such as the unity of all, and the unreality of time – are common, shared objects of experience under the psychedelic influence.
• Coherence with other beliefs: An object perceived through the senses that does not cohere with one's network of prior beliefs will often be dismissed as unreal. Of course, this is not a strong criterion for veridicality as one's prior beliefs may be false as they are often inculcated rather than developed through reason.
• Rationality: If we have background rationale for believing in the veridicality of that which we experience, we are thereby prone to consider the experience as veridical. For example, we may have reasons to doubt the reality of time. Moreover, if we can show that the objects of experience are logically coherent and not contradictory, their veridicality is shown to be possible.

None of these criteria for veridicality refute the veridicality of all psychedelic experiences. Yet they neither prove their veridicality. But, the fact that many types of psychedelic experience have shared objects of experience – such as the unreality of time, or the unity of subject and object – is suggestive of veridicality. The Cambridge philosopher CD Broad argued that, 'So far as [mystical experiences] agree they should be provisionally accepted as veridical unless there is some positive ground for thinking that they are not.' The 'positive ground' given by the sceptic theist is that the experiences, (i) are caused by a drug's effects alone, and (ii) do not cohere with their religion. The 'positive ground' of the physicalist is the same (i) as above, and (ii) that they neither cohere with their creed. 

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"If only I see the lamp, but others do not, I may question the veridicality of my experience. But the experiences of grander psychedelic phenomena listed above - such as the unity of all, and the unreality of time - are common, shared objects of experience under the psychedelic influence."

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We have seen above that (i) is not a positive ground: chemically-induced correlates of mystical experience cannot per se disprove the objectivity of that which is experienced. With regard to (ii), let us consider the creed of the physicalist. This creed claims, in brief, that all that fundamentally exists is matter-energy, spacetime, forces of nature, and laws of nature. Sometimes its adherents refer to themselves as 'naturalists' and their detractors as 'supernaturalists'. But as contemporary philosopher Galen Strawson notes, 'One can't ... classify anything as supernatural or nonnatural until one has an account of what is natural.' And physicalism cannot account for that which is most natural to each of us: consciousness.

Some strands of physicalism believe that consciousness does not exist – but this is a performative contradiction (belief in the unreality of belief). Another strand believes that consciousness emerges from matter, but how and by which laws of nature this occurs is never explained. We must realize that correlation is not explanation. Philosopher of mind Jaegwon Kim reminds us that, '[m]aking a running list of psychoneural correlations does not come anywhere near gaining an explanatory insight into why there are such correlations'. There is no observable causal line between a neuro-physical motion and a conscious emotion. Another strand of physicalism identifies mental states with neuro-physical states. But the properties of each type of state are so dissimilar that such identity is rejected on logical grounds.

Furthermore, mental causation – that a thought or desire can cause a bodily movement or trigger a further mental change – cannot be explained via physicalism yet to deny it would be to render mentality impotent, useless, which would be contrary to both evolutionary and logical principles. These old problems, and others, are encapsulated in the new term, the hard problem of consciousness. In truth, the hard problem of consciousness is a disproof of physicalism. Physicalism cannot account for consciousness, therefore it cannot be an adequate understanding of reality. Thus the fact that psychedelic experiences do not cohere with the physicalist’s view of the world should not lead us to think these experiences are non-veridical.

There appears, then, to be no obvious positive ground for thinking that certain shared psychedelic experiences are not veridical. Moreover, if we shift from theories physical up to theories metaphysical, we gain further reasons other than shared experience and noetic feelings to accept certain psychedelic experiences as revelatory, as revealing deeper truths.

For instance, the metaphysician Spinoza argued that mind and matter were but different attributes of the same unified substance: 'God' or 'Nature'. Bertrand Russell wrote that '[o]ne of the most convincing aspects of the mystic illumination is the apparent revelation of the oneness of all things'. If one accepts Spinoza's monistic philosophy, as Einstein did, then such a unitive experience under the influence would be very plausibly veridical. In fact, Spinoza himself spoke of a mysterious form of perception he named amor dei intellectualis, ‘the intellectual love of God’, an experience that was the ‘highest possible peace of mind, that is to say … the highest joy’. God for Spinoza was Nature itself. Thus the unitive and pantheist experiences common to psychedelic states have solid grounds for veridicality in this metaphysics.

Spinoza once met the great inventor of both the calculus and the calculator, G. W. Leibniz. Leibniz was known for his Monadology: the view that not only humans, mammals, and the more complex animals have mentality, but also the insects, plants, micro-organisms, etc., all the way down. This is a form of panpsychism: that sentience lies within all things that are units, or monads (but not aggregates, such as rocks and socks). Panpsychism is a metaphysical view gaining prominence once more today, and again lends itself to substantiating the veridicality of certain psychedelic experiences concerning the sentience and intrinsic value of all the entities of nature.

Thus we see that one’s underlying ideology determines whether or not we understand psychedelic experiences as hallucinations or revelations. The ideology, or faith, of physicalism prevalent today cannot endure as it cannot explain consciousness, let alone psychedelic consciousness. On the other side, believing that everything one perceives in the psychedelic state to be veridical is obviously also too much, considering that certain phenomena are never shared. It would be implausible to believe in the veridicality of the particular spider that conversed with an artane-inebriated Oliver Sacks 'mostly on rather technical matters of analytic philosophy'. No, the plausibility of the veridicality of psychedelic experiences depends on their having a shared type of experience, one that is coherent with a rational metaphysics, and which can be further fortified by a concurrent noetic feeling. This is what better determines whether a psychedelic experience is considered revelation or hallucination.

In fact, it may have been such mystical experiences that sired the preference for certain metaphysical frameworks of understanding, above physical ones alone. One seeks to rationalize what one experiences. As Bertrand Russell, who wrote a book on Leibniz, put it in his essay, 'Mysticism and Logic':

'Metaphysics … has been developed, from the first, by the union and conflict of two very different human impulses, the one urging men towards mysticism, the other urging them towards science.'

References

James, W. The Varieties of Religious Experience 

Paz, O. Alternating Current, trans

Donovan, P. Interpreting Religious Experience 

For instance, Zaehner, R. C. Mysticism Sacred and Profane. For a specific rebuttal of Zaehner's view, see Price, H. H. 'A Mescaline Experience', Journal of the American Society for Psychical Research

McTaggart, J. E. 'The Unreality of Time', Mind

Broad, C. D. 'Arguments for the Existence of God II', The Journal of Theological Studies

Strawson, G. 'Real Naturalism', London Review of Books

Kim, J. Physicalism, or Something Near Enough 

Bradley, F. H. 'On the Supposed Uselessness of the Soul', Mind

Popper, K. 'Natural Selection and the Emergence of Mind', Dialectica

Kim, J. Essays in the Metaphysics of Mind 

David Chalmers, 'Facing up to the problem of consciousness', Journal of Consciousness Studies

Peter Sjostedt-H.  'Why I am not a Physicalist: Four Reasons for Rejecting the Faith', The Side View

Russell, B. 'Mysticism and Logic ', The Hibbert Journal, repr. Mysticism and Logic and Other Essays 

Spinoza, B. Ethics, trans. W. H. White and A. H. Stirling.

For instance, see: https://highexistence.com/panpsychism-3-reasons-why-our-world-brimming-sentience/

Sacks, O. Hallucinations 

Russell, B.  'Mysticism and Logic ', The Hibbert Journal; repr. (1918) Mysticism and Logic and Other Essays