Treating psychedelic experiences as epistemically transformative provides a usefully nuanced conception of how psychedelics induce metaphysical beliefs. However, as it stands, this conception is incomplete as an account of how psychedelic states can have a rational bearing on one’s view of the ultimate structure of reality.

For starters, notice that the epistemic transformations that Paul discusses in her seminal work involve the acquisition of beliefs about what it is like to have certain conscious experiences (like the ones associated with becoming a parent, participating in a war, or acquiring a new perceptual modality; see Paul 2014). These are beliefs about subjective facts, that is, facts that become accessible by virtue of a person having the relevant sort of experience. But Mary’s case is different. What she purportedly learns from her psilocybin session is not exhausted by the knowledge about what it is like to undergo a mystical experience. Mary claims to have learned something about the structure of reality. A question arises about whether and how a psychedelic state could be world-revealing.

Relatedly, notice that the mere fact that one had a purportedly world-revealing transformative experience does not by itself establish a rational link between this experience and the resulting beliefs. Consider two ways in which an epistemically transformative experience might fail to provide good reasons for belief. One involves brute transformations that bypass cognitive processes of the sort that could be epistemically relevant. Think of acquiring beliefs through participating in a Clockwork Orange-style aversion therapy. The second type of faulty transformation is epistemically evaluable but also epistemically bad. Think of Bayesian models of delusions acquired during a psychotic episode (see Fletcher, Firth 2009 for a classic exposition). These models take delusions to be formed and maintained through (unconscious) Bayesian inference. However, this inference is epistemically compromised by systematically overestimating the evidential value of sensory data.Footnote 4

I want to argue that psychedelic epistemic transformations are neither brute nor bad in this way. For this purpose, I will take an epistemologically-oriented look at the dominant scientific model of the cognitive underpinnings of psychedelic states. This is the REBUS model, dubbed using an acronym for “RElaxed Beliefs Under pSychedelics” (Carhart-Harris and Friston 2019). I will argue that under the REBUS model, psychedelic states are capable of being rationally integrated with one’s belief system.Footnote 5 Later, in Sect. 3.2 and 3.3, I will return to the question of psychedelic experiences as world-revealers.

The REBUS model employs the idea that the brain is a Bayesian system. In particular, it rests on the predictive processing (henceforth PP) variant of the Bayesian brain hypothesis. PP has become a major theoretical framework within contemporary cognitive (neuro)science, so I expect many readers to be at least cursorily familiar with it. Because of this, and due to the limitations of space, what I provide below is a bare-bones summary of PP (for up-to-date introductions, see Hohwy 2020; Parr et al. 2022).

The crux of PP lies in treating the brain as an “inference machine” comprised of hierarchically organized information processing mechanisms. Each level of the hierarchy has one computational goal: to calculate the posterior probability of some hypothesis or estimate, \(p\left(h|d\right)\), through approximating Bayesian inference. The hierarchy encodes a generative model whose function is to capture the world’s nested causal structure and the way this structure produces patterns of sensory data in the organism. At each level, the generative model encodes a joint probability of hypotheses and lower-level (ultimately, sensory) data, \(p(h, d)\), which is factorizable into a product of the prior, \(p\left(h\right)\), and the likelihood, \(p\left(d|h\right)\). Equipped with the generative model, the brain is thought to engage in a variational approximation of Bayesian inference. Roughly, the brain uses the model to generate an estimate of the state of the world and iteratively brings this estimate closer to a true posterior that an exact Bayesian inference would yield (under the model). Mechanistically, this is realized by a bidirectional information flow comprised of top-down prediction signals and bottom-up prediction error signals. The task is to minimize average prediction errors across the hierarchy.

I will assume that to the degree that PP captures the computational structure of cognition, it renders this structure epistemically evaluable. This is because, under PP, the causal evolution of the brain’s representation of the world approximately conforms to a rational rule of inference (Gładziejewski 2021). For example, in the case of perception, PP renders perceptual states epistemically evaluable by treating them as inferentially derived from prior and likelihood distributions encoded in the generative model (Gładziejewski 2021). This effectively constitutes a variant of Susana Siegel’s “rationality of perception” approach (Siegel 2017).

I will further assume that the processing invoked by PP can remain epistemically relevant under a systematic disruption. Imagine a procedure that tinkers with the values of priors encoded in the generative model or with how precise or reliable these priors are estimated to be. Now, as long as the processing remains approximately Bayesian under this procedure, it remains epistemically appraisable (hence, epistemically relevant).

One last assumption I will be making going forward is that the processes invoked by PP remain epistemically appraisable when they run off-line. I am referring here to the idea that the generative model can become decoupled from the current sensory stream and used to run internal simulations of non-actual scenarios (Williams 2021). Such processing is rationally constrained by the generative model because the flow of the simulation is determined by the model-encoded assumptions: the brain samples sequences most-likely-under-a-model. I take this type of off-line processing to be epistemically evaluable (for a view that makes a similar case independently of PP, see e.g. Myers 2021).

Now, onto the REBUS model. PP treats perception as an interplay between top-down cognitive structures and bottom-up error signals. The relative degree to which processing is determined by prior knowledge and the incoming error signals is flexibly determined through precision estimation. Precision measures the inverse variance of priors and error signals, effectively tracking their relative reliability. Now, by acting on the serotonin 5-HT2A receptors of deep pyramidal cells in the cortex (which are thought to encode priors), psychedelic compounds decrease the precision of priors (Carhart-Harris and Friston 2019). This way, they reduce the degree to which prior cognitive structures normally constrain and regulate cognitive activity. Hence, the priors harbored in the brain’s generative model become “relaxed”.

Relaxing of priors affects the inferential processes involved in perception, inducing perceptual distortions and hallucinations. However, perceptual changes are a relatively unimportant feature of the phenomenology of acute psychedelic states that I am interested in here. (Quite literally, in therapeutic settings, participants in psychedelic sessions are usually invited to go through the experience with their eyes closed). These states are dream-like or imagination-like in the sense of being endogenously constructed. So, in light of REBUS, deep psychedelic states consist of a free flow of internal constructions that is unconstrained, or significantly less constrained, by the priors that regulate regular cognitive operation. Upon entering a psychedelic state, the dysregulated generative model runs off-line in a way that allows it to venture into new regions of the representational state space.

Importantly, this psychedelic-induced cognitive disruption does not undermine the status of the brain as a Bayesian system. On the REBUS model, the psychedelic-influenced brain remains Bayesian, even if it runs on relaxed priors. Arguably, this is reflected in phenomenology: far from being experienced as a random mess of cognitive junk, deep psychedelic states are usually described as possessing an intelligible (even if ineffable) structure. So, given all these considerations, I propose that psychedelic epistemic transformations are not brute. They reside within the domain of normatively relevant cognition.

My further claim is that acute psychedelic states possess the power to improve the epistemic standing of one’s beliefs. What does this rational role consist of, exactly? The claim is not that it can be pinned down to a particular chain of justification-conferring inference. I do not mean to suggest that the processing that takes place in a psychedelic state is somehow epistemically better than normal cognitive operation. Rather, to understand my point, we need to take a wider perspective on the epistemic life of a person, and on how transient, psychedelic-induced disruptions of this life can be epistemically beneficial in the long run. To a first approximation, the claim is that one can improve the epistemic standing of one’s conception of oneself and the world by occasionally wandering off the beaten cognitive path to consider previously unconceived alternatives. Psychedelics constitute a tool that reliably elicits such an exploratory mode of cognition.

This view of psychedelic epistemology is already discernible in how Robin Carhart-Harris and Karl Friston (2019) frame the REBUS model. To explain how psychedelic states can be therapeutic, they point to the process of relaxing the precision of “pathologically overweighted” priors. These are psychologically harmful priors so deeply entrenched into one’s internal model that they become resistant to revision. When this is the case, one’s model of the world gets stuck in a local minimum of the free energy (prediction error) landscape. By relaxing the precision of priors, which is equivalent to opening or flattening the free energy landscape, psychedelics allow the model to get instantly “unstuck”. To give a high-level example, in a psychedelic state, priors that underlie one’s narrative self-conception may become relaxed. This, according to REBUS, allows one to turn a debilitating self-narrative into a new, positive, but also more realistic conception of who one is. Now, there is an epistemic side to this story as it is plausible to assume that the newly gained self-conception is more well-grounded or accurate than the previous one (see Letheby 2021, Ch. 8).Footnote 6

Let me now try to make this more systematic. Aronowitz (2021) has recently proposed that we should extend our concept of epistemic rationality in a way that takes into account an exploration/exploitation trade-off that arises at the level of belief. The exploration/exploitation problem originally applies to adaptive action. Roughly, the idea is that organisms face the choice between exploiting existing strategies for successful behavior and trying out new strategies that could, with some small but non-negligible probability, prove even more successful in the long run (should I order my favorite dish at a restaurant or risk trying out something new?). In a complex world where the reward function cannot be known in advance, it is good to adopt a strategy that mixes exploitation with some degree of exploration.

Aronowitz proposes that we face a structurally similar exploration/exploitation dilemma in our epistemic lives, in the following sense. At least some of the things we learn, or novel hypotheses we invent, we arrive at through the exercise of mental simulation. How these internal simulations unfold is guided by our beliefs (see also Myers 2021; Williams 2021). However, beliefs not only guide but also limit our mental constructions in epistemically relevant ways. That is, we may miss some relevant possibilities because they are obstructed by the beliefs that constrain, often implicitly, the imaginative search. So, it may be epistemically valuable to sometimes adopt other beliefs even if they are undersupported by current evidence.Footnote 7 This is because the different beliefs may guide the simulation-based inquiry to previously hidden truths. The upshot: to create an opportunity for learning and accuracy in the long run, it is rational to mix some degree of epistemic exploration into one’s epistemic life.

I propose that this story can be extended to cover the rational role of psychedelic states. According to the REBUS model, psychedelics elicit a sort of exploratory simulation in which alternate priors are flexibly “tried out”. In fact, it may be said that psychedelic states constitute a radical form of exploration. Aronowitz’s original proposal is oriented towards epistemic exploration insofar as it is guided and constrained by personal-level beliefs. Psychedelics reach deeper into cognitive architecture by targeting subpersonal priors. As will transpire in the next subsection, this includes priors that constrain our imagination in ways relevant to the metaphysical inquiry. In any case, the basic normative upshot of Aronowitz’s proposal still stands in the present context. It is rational to sometimes put oneself in an epistemically risky position that provides an opportunity to learn something new and otherwise unavailable. The rational role of psychedelic states consists of eliciting bursts of such exploration.

Importantly, this is not to say that mere engagement in the psychedelic exploration of consciousness automatically generates warrant for metaphysical beliefs. The point is that epistemic exploration through psychedelic states is valuable even if many (perhaps most) of the new cognitions turn out of little epistemic value (see McGovern et al. 2023). For comparison, at the level of action, most acts of exploration may fail to bring about outcomes that outperform the exploitation of previously leaned policies. Still, exploration is valuable in virtue of enabling the learning of novel policies over longer time spans (and only when appropriately mixed with the exploitation of previously learned action policies). Similarly, the value of epistemic exploration through psychedelic states lies in how it enriches the inquiry process, where the subject actively seeks and evaluates evidence about a subject matter before stable beliefs are crystallized (Friedman 2019). For illustration, consider the physicist Carlo Rovelli, who recounts how early experiences with LSD guided his thinking about the nature of temporal passage:

It was an extraordinarily strong experience that touched me also intellectually. Among the strange phenomena was the sense of time stopping. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing anymore. It was a total subversion of the structure of reality. (…). And I thought: “Well, it’s a chemical that is changing things in my brain. But how do I know that the usual perception is right, and this is wrong? If these two ways of perceiving are so different, what does it mean that one is the correct one?” (From Higgins 2018).

Now is the time for the discussion to directly connect with metaphysics. Can exploring non-ordinary forms of conscious experience deliver results that are evidentially or justificationally relevant for beliefs regarding the ultimate structure of reality? For starters, let us recognize the evidential role that ordinary experience plays in metaphysical inquiry. Think in particular of visual perceptual experience which purports to reveal a world that flows through time, furnished with macroscopic objects occupying determinate positions in a three-dimensional space. Visual experience also seems to spring from a subjective point of view, arguably revealing an experiencing self that flows through time along with the experienced world. In this fairly innocent sense, already implicitly embedded in ordinary experience, there is the commonsense metaphysics of the manifest image (Sellars 1963).

Ordinary experience serves as a source of defeasible data for metaphysical inquiry (Benovsky 2015; Goldman 2015; Paul 2012). In some cases, the relevant aspects of ordinary consciousness become explicitly invoked as potentially decisive in settling a metaphysical problem. Take the debate regarding the reality of the passage of time. Realists about temporal flow think that there is an evermoving, metaphysically privileged present moment and that whatever is located in the past or the future relative to this moment lacks proper existence. Why should we believe such a view? Here, realists often point to the temporal structure of ordinary experience (see Paul 2010 for discussion). According to this line of thinking, what justifies the belief that time flows is that the sense of temporal passage is a pervasive aspect of conscious experience.

Consider also how imagery can be evidentially relevant for metaphysics. Here, by “imagery”, I mean the capacity to re-use our perceptual and action-guiding machinery for off-line cognition. It has been argued that such internal simulations can act as a source of modal knowledge (see e.g. Gregory 2020; Kung 2010; Williamson 2007). Very roughly, the idea is that (un)imaginability can be a guide to (im)possibility. Think of how a modal fact about consciousness itself might be claimed to be discovered through an exercise of imagination. I find myself utterly unable to imaginatively simulate a timeless mental state, a state that lacks the sense of temporal flow. From this, I might infer that atemporal consciousness is impossible. This, in turn, might lend additional modal weight to the “argument from experience” regarding the objective passage of time. On this construal, by pointing to our experience as evidence in favor of objective temporal flow, we are not simply pointing to a contingent fact about the conscious experience of a particular hominid species, but to a structure that any conscious experience must necessarily possess.

This is where PP and the REBUS model may reenter the picture. According to PP, the metaphysically relevant aspects of ordinary perceptual phenomenology—the self, the flowing time, the space, and the ordinary objects contained in it—are generated by the inferential machinery that underpins perception. The idea is that at the highest levels of the generative model, the brain stores abstract “hyperpriors” that put very general (“almost Kantian”, Clark 2016, p. 174) constraints on the cognitive activity at lower levels. To make the discussion tractable, let me narrow the focus to the priors that are thought to underlie the sense of self and temporal passage. The sense of self has been theorized to result from a process in which the brain infers a single endogenous cause underlying short-term correlations in body-related signals (the embodied aspect of experienced selfhood) and long-term sensory patterns (the narrative aspect of self; see Hohwy and Michael 2017; Letheby 2021, Ch. 7; Letheby and Gerrans 2017). The sense of temporal passage has been argued to be grounded in a high-level prior expectation of the world and the sensory signal caused by it to be constantly changing (Hohwy et al. 2016).

Now, according to the REBUS model, psychedelic compounds target these metaphysically relevant hyperpriors, relaxing them—sometimes to the point of altogether dissolving them—without eliminating the conscious experience itself. This way, they elicit an experience that differs from everyday consciousness at the level of core organizing principles. But more pertinently for the present purposes, psychedelic states are evidentially relevant because they broaden the range of data that can guide and constrain metaphysical inquiry. Insofar as we draw on the structural properties of consciousness to inform our metaphysics, psychedelics allow us to pool data that go beyond the confines of the default structure of experience.

In at least two ways, this widening of available evidence could undermine or problematize metaphysical views rooted in ordinary experience. For one thing, psychedelic states may directly falsify modal claims grounded in (ordinary) imagination. Once the prior underlying the sense of temporal flow is discarded, one can venture into a region of one’s representational state space that would typically be inaccessible. Quite literally, one gains the capacity to construct an experience that lacks the sense of temporal flow. This way, psychedelic experiences of “eternity” falsify the idea that the sense of temporal passage is a necessary structure of any conscious experience. This, in turn, strips the experience-based argument for the objective temporal passage from its modal force.

Another way in which psychedelic states can play this sort of commonsense-undermining role is by providing first-person data in support of the idea that certain core features of normal experience are not innocently given but are actively (even if unconsciously) constructed (see also Letheby 2021, Ch. 7). For example, by undergoing a psychedelic state in which one’s very sense of self is dissolved, one arguably learns that one’s usual sense of self is a result of interpretation or (unconscious) inference. Now, the fact that the experience of being a self is somehow constructed does not by itself establish it as non-veridical. But it invites a view on which the very sense of self is epistemically assessable depending on the nature of processes that give rise to it. It can no longer act as an unjustified justifier of metaphysical claims about the self (Gładziejewski 2021). To generalize, following a deep psychedelic experience, it arguably becomes harder to remain foundationalist about the posits of the manifest image.

But I think that the value of psychedelic states goes beyond undermining or problematizing existing evidence. Psychedelic experiences also provide new data. Think of a role that psychedelic-induced mystical(-like) states could play when considered not in and of themselves, but when embedded in a wider discursive structure. Let us focus on a particular case of cosmopsychism, a monistic version of panpsychism or idealism. Roughly, the view is that consciousness is metaphysically fundamental and that the world, including individual human subjects, is grounded in a single, universal consciousness. Although still somewhat fringe, this view has recently gained some traction among philosophers (see e.g. Albahari 2019; Shani 2015; see also essays in Seager 2019).

Cosmopsychism is often theoretically motivated by the Hard Problem of Consciousness and advertised as a less problematic alternative to standard forms of panpsychism. But it faces hefty philosophical problems of its own. Can we make sense of consciousness that extends beyond individual subjects of experience? And how can such an all-encompassing consciousness ground or “decombine” into the multitude of apparently separate minds? Some authors have suggested that (1) universal consciousness is aperspectival, lacking any subject/object division, and (2) individual subjects of experience can be deflated as somehow illusory, whereby subjective points of view arise from relations between experiences rather than by being related to persisting individual entities or “selves” (for relevant discussions, see Albahari 2019; Chalmers 2019).

The problem with this proposal is that it is not easy to make concrete sense of the theoretical posits it invokes (see Chalmers 2019, p. 367). Of course, a philosopher may posit on purely theoretical grounds that there are forms of consciousness that are “non-dual” with respect to subject/object division, thus constructing an internally coherent picture of ultimate reality. But there is a worry that independent reasons or data should be provided to “externally” validate the central theoretical posit, i.e., that there can be phenomenal states that transcend subject/object duality. This is where altered states of consciousness become relevant. Through dissolving priors that underpin the sense of self, psychedelic compounds can elicit states of consciousness that are unstructured along the subject/object distinction. As such, these experiences play crucial evidential roles in the present context by providing missing data. On a weaker reading, they make the very idea of cosmopsychism conceivable: “If consciousness can conceivably be experienced as aperspectival and unconditioned, then, being inherently experiential, it will conceivably be aperspectival and unconditioned” (Albahari 2019, p. 14). But on a stronger reading, these experiences can be interpreted as directly confirming the belief in conscious states with non-dual phenomenal character, which is a significant improvement over postulating such states based solely on theoretical considerations. This, by itself, does not establish that non-dual consciousness grounds individual conscious subjects. However, at least it adds support for the belief in the existence of the former, more exotic relatum of this postulated grounding.

Before I move on, let me mention one last potential epistemic benefit of psychedelic states. By their nature, revisionary positions in metaphysics tend to be misaligned with the ways in which humans spontaneously experience and conceptualize the world and themselves. For illustration, consider again the question of the existence of the self. Albahari (2014) discusses a case of a person who (1) forms, on purely theoretical grounds, a “reflective” belief that there are no selves, but (2) her conscious experience remains subjectively centered around a stable, continuous self, resulting in a cluster of cognitive, emotional and behavioral dispositions (for example, self-related anxieties) that Albahari calls “action-based” belief. Now, Albahari argues that accomplished Buddhist meditators systematically alter their consciousness to gain direct experiential insight into no-self. This, in effect, brings them into a state of increased cognitive coherence, whereby their spontaneous dispositions no longer contradict their reflective beliefs about the (purported) illusion of self. I think that psychedelic states can play a similar role by enabling a person to achieve cognitive coherence with respect to views about, for example, the non-existence of selves or the existence of non-dual forms of consciousness.Footnote 8

There is one more issue that requires addressing—that of the veracity of acute psychedelic experiences. Skeptics about the metaphysical import of psychedelic states may still question the idea that these states could reveal metaphysical facts. Let me now sketch out a view of how acute psychedelic states could be on-track with respect to at least some metaphysical truths.

We need to distinguish two models of how psychedelic states could be truth-revealing. The first model—the “third eye” model—treats psychedelic states as akin to perception, construed along foundationalist lines. According to this picture, in a deep psychedelic state, one’s “mystical sense” or “metaphysical truth detector” is opened to put one in direct epistemic contact with ultimate reality. Instead, I want to suggest the alternative, the “dispelling-the-illusion” model. This view rests on the assumption that at least some cognitive structures that give rise to the manifest image are systematically off-track with respect to metaphysical truth. In a psychedelic state, those truth-obstructing cognitive structures are removed, allowing one to enter a conscious state that better aligns with how the world is.

Here is how the dispelling-the-illusion model might work. We may start by noting that there is a growing body of work in philosophy and cognitive science defending the view that default perceptual and cognitive structures are off-track with respect to metaphysical truths (see e.g. Benovsky 2015; Goldman 2015; Ladyman and Ross 2007, Ch. 1; Korman 2019). This may mean that at least some aspects of default cognition are either (1) limited to selectively revealing only truths that are available from the perspective of a particular type of organism, like a human (weaker claim), or are (2) altogether off-track with respect to metaphysical truth (stronger claim). In any case, the core assumption of the dispelling-the-illusion model is not implausible. Hence, by relaxing or dissolving default priors that constrain perception, psychedelics could remove cognitive structures that normally obstruct the truth. Instead of opening up a new, mystical perceptual-like “modality”, psychedelics disrupt the existing inferential machinery in a way that may bring it closer to accurately capturing (the relevant parts of) reality.

For illustration, consider again two aspects of ordinary experience that shape the manifest image: (1) the experience of temporal flow and (2) the experience of one’s perception and conscious thoughts as originating from and being centered around a persisting individual self. Three types of considerations favor viewing those aspects of ordinary consciousness as illusory. First, and weakest, general evolutionary considerations dissociate the adaptiveness of a cognitive mechanism from its ability to represent the world truthfully. Second, there are plausible explanations of the subjective sense of temporal flow and selfhood on which neither of those experiences reflects the way the world really is. The experience of temporal flow can be explained by positing a temporally ordered (but not temporally flowing) sequence of states whose phenomenal character generates the illusion of temporal passage (Paul 2010; Price 1996, pp. 14–15; Le Poidevin 2007). The experience of being a persisting self can be explained by a binding process that gives rise to the sense of being a simple, substance-like entity without actually tracking any such entity (Letheby and Gerrans 2017). Third, and perhaps most importantly, there are strong scientific and philosophical cases to be made against temporal passage and selves. For temporal flow, forceful arguments have been proposed in favor of eternalism, the view that denies that the world fades and becomes as the window of “now” moves. Eternalism has been repeatedly argued to find support in “block” models of the universe rooted in relativistic physics (Barbour 1999; Carroll 2010; Price 1996). For self, philosophical arguments have been put forward against the view that there exists an enduring entity that corresponds to what people ordinarily identify as selves (Nāgārjuna 1995; Parfit 1995).

So the point is that by relaxing or dissolving default priors that constrain perception, psychedelics could be removing cognitive structures that normally obstruct the truth. Instead of opening up a new, mystical perceptual-like “modality,” psychedelics disrupt the existing inferential machinery in a way that may bring it closer to accurately capturing (relevant parts of) reality. I think there are strong reasons to think that this happens during the psychedelic-induced dissolution of the experience of being an individual self, flowing through time. Under eternalist and no-self metaphysics, selfless and timeless experiences are better aligned with ground truth about reality.

However, even given all of this, there is a substantial worry to be raised hereFootnote 9. Why not simply claim that psychedelic states make people bump from one illusion to another (see McGovern et al. 2023)? Or, why regard such states as somehow geared towards revealing truth rather than, at most, moving us from falsehood to truth by sheer epistemic luck?

Here, I do not have a definitive answer. However, let me sketch out three possible directions in which one could proceed here (two of which arguably revert us to the third-eye model of psychedelic epistemology). One would be to sidestep truth as such and go foundationalist in one’s epistemology, arguably sticking in this respect to mystical traditions. Roughly, the claim would be that, ultimately, any knowledge can only be grounded in conscious experience, like perception or intellectual intuition. In the present context, this basic view could be combined with the notion that what imbues specific experiences with the power to act as an ultimate source of justification, absent defeaters, is their noetic quality or subjective sense of truthiness (see e.g. Tucker 2011). Then, one could claim that the noetic quality of mystical experience outstrips other forms of experience (save perhaps mathematical intuition). Hence, all else being equal (i.e., absent defeaters), mystical-experience-based beliefs have a stronger claim for being true or constituting knowledge than (almost) any other type of belief. The downside of this option is the problematic epistemology it is based on (Gładziejewski 2022), including the crucial issue of whether all else is indeed equal in the particular case of mystical states.

Another option would be to construct a more comprehensive philosophical view of mystical experience that renders it more “truthy” than ordinary experience. If reality is ultimately grounded in universal consciousness, then experiences of cosmic unity could count as cases in which an (apparent) individual discovers her deeper, true identity – by dissolving into it. On such a picture, there seems to be a direct connection between the content of the mystical experience and the ground truth about reality. The obvious drawback here is that such treatment presupposes the very metaphysical view that the non-ordinary experience is supposed to support.

However, I think that the most reasonable option is much more modest. No experience, ordinary or altered, carries with itself the information about its ultimate origins (consider radical skeptical scenarios). To ascertain the value of experience, we need to look beyond it. Whatever evidence non-ordinary experience delivers, the move from experience to belief should be mediated by consulting other strains of evidence. That is, the crucial question is whether what psychedelic states deliver converges with what is supported by other lines of inquiry. By “other lines of inquiry”. I mean science and philosophical arguments of a more a priori kind. In some cases (e.g., the self, temporal passage, and arguably also cosmopsychism), we may find non-trivial convergence. In other cases, there is no discernible convergence, and the move from experience to belief requires one to overrule other forms of evidence or reach beyond what they allow to rationally believe. Trans-dimensional DMT entities may belong to this category. Such latter cases are epistemically problematic in a way that the former are not. For those who are compelled by the idea of psychedelic-induced mystical states as epistemically privileged gateways to ultimate truths, this sort of coherentist picture might sound too minimalistic. However, I suspect this is as much as we can get as long as we remain loyal to considerations of epistemic rationality.