Hallucination vs Reality

The Differences Between Hallucination and Reality Can Be Minimal

This article about hallucination vs reality is more philosophical in nature than medical, yet very relevant to the issue of psychosis or schizophrenia. I will attempt to use common vernacular when possible; however, at times I will be compelled to use the nomenclature of philosophy to explain a position or view. I will even raise some issues that challenge our commonsense views of reality, existence, and life; but this is good and we can all learn from probing some of these weighty philosophical issues. I believe that understanding one of the leading theories of perception viz. representative realism will show us how the mind perceives the world and how easily it can be “tricked”. Understanding this will then show us how real a hallucination or illusion appears to someone suffering from psychosis, and maybe assist us in convincing or teaching someone how to discern between hallucinations and reality. After we briefly discuss this truncated discussion of representative realism I think you might be surprised how close a hallucination is to reality. There are other popular views of epistemology viz. phenomenalism which postulates that everything is illusion, but if I succeed in presenting this theory of perception, you too may begin to question what is real and how can you justify your belief?

Marie Gronley, MD

As a psychiatrist in Scottsdale I treat schizophrenia and schizoaffective disorder, often with positive results. One of the greatest challenges in dealing with a patient having a form of psychosis is to convince them that what they may hear, smell, see, or think; are hallucinations and have no basis in reality. The problem, I believe has to do with perception and how the mind corresponds to the extended world or reality.

We see this image or sense datum but not the real world

As humans we cannot know the extended world (reality) intrinsically. This is one thing that all philosophers agree on. Nobody will ever know what subsumes sub-sub-sub-sub atomic particles or quarks, the items which ultimately constitute all matter and reality. I can say this with certainty because we will never know “when we reached the bottom”, or have found the primitive substance of which matter is made of, but I digress. This view excludes the theory of naive realism which would not be apropos to the discussion. Nobody can know the world outside of their humanity. What I mean by this is that we cannot know the world in an unbiased fashion apart from our senses and human limitations. These biases are based on our senses, our minds, presuppositions, and worldviews. Nobody can make a claim to possessing brute facts of science, the world, or anything of the empirical realm. All we can know is what our minds experience based on the mediation of several factors.


For example we see a moth, yet what does a Fruit Bat see when a moth is presented to its senses? Descartes summed this up in his cogito viz. “I think therefore I am”. Descartes knew the only thing we could indefeasibly know was that we exist, beyond this we cannot prove anything else because we don’t have privileged access to an objective view of the world. Even David Hume wrote: “Tis vain to ask if there be a body”. Hume said it was impossible to prove that there is an extended world-yet we believe it exists, we just can’t find an incorrigible thesis to prove it. You may detect I am laying some groundwork to exhibit that reality is not a settled fact and the line between hallucination and reality is much thinner than most of us believe. Hallucinations and reality share a lot in common, and this is the difficulty of convincing someone that their beliefs, thoughts, and what their senses tell them are not always true.


Consider that no two people can see, smell, or hear the exact same thing – everyone’s understanding of reality is different. We might go as far as to say that reality is an issue of convention or agreement, or what the majority deems normal. This is called the naive realism or commonsense theory of epistemology or perception.

We Cannot Perceive the Differences Between Hallucination and Reality Except for the Empirical Evidence that Causally Ground our Beliefs

What we perceive about the world is really seen through our conceptual framework and senses, which according to the theory of representative realism or indirect realism; all that we know of the world is mediated through sense datum. We don’t necessarily see things as they are but as what our humanity enables or limits us to see, mediated by the sense datum (image). Remember that what we see as a moth, a Fruit Bat might see as a radar blip. To further demonstrate this let’s begin with color. Does color exist (talking about color not light frequency)? No, color does not exist apart from a sentient being having the ability to look at some molecules that possess dispositional properties or the powers to reflect a frequency of light. This light is then perceived through the rods and cones in the eyes which then convey this information or image (sense datum) to the mind. So we perceive color indirectly which is mediated through light, our senses, and ultimately through sense datum or images.

Back to the issue of convention, if everyone were color blind, then nobody would see any color, hence color would not exist. This is the same as the proverbial conundrum “If a tree falls in the forest and there is nobody there to hear it; did it make a noise?” Again the answer is no. There may have been shock waves rippling through the air but if there is no sentient being with ears to hear it, then there is no “noise”. Again we have an example of our perceiving the world indirectly through sense datum (in this case the sense datum is sound) and not perceiving the world directly or intrinsically.

How about objects? Let’s assume that five of us are sitting around the coffee table and we see an apple on the table, do any of us see the same thing and are we seeing what is really there? What we see is an image or sense datum that exists some where between (or in) our minds and our senses. If this image or sense datum is causally linked to an molecular structure in the location of the image; then we would say the apple truly exists. Yet what we see is not intrinsically real but rather what our humanity limits us to see. So we might conclude that our reality is mediated by an image that our mind creates through our senses which is provoked by an object in the real world which has a causal influence or power to produce the sense datum which is presented to our minds. This theory of representative realism is a causal theory in that it relies on there being a causal connection between these atoms that occupy time and space and the image (sense datum) that we see being presented to our minds through our senses. Are you still with me? So far we can conclude that for an image to be real it must be grounded in a causal connection between atomic matter that occupies the space where the image is perceived, and a causal relationship between this matter and the image which it corresponds to; otherwise the image is an ungrounded hallucination and would be said to have no basis in reality – yet this hallucination is sort of a “partial truth”. Partial because the sense datum or image is presented to the mind, yet without a causal link to something extended in space.

Often Hallucinations Mirror Reality And Are Difficult to Discern One From The Other

The problem with a psychotic experience is that in many cases the individual perceiving the hallucination sees exactly what we would see, only there is no causal link between the image and any molecular structure occupying the time and space of the image. We too often think that these hallucinations are like mirages, blurry, or surreal; however, that’s not always the case. When someone sees, hears, or smells something, it’s either causally related to some atomic structure in the extended world which grounds its reality or it’s not, and is a mere hallucination. This is the subtle demarcation of hallucination vs reality.

A person suffering from psychosis who claims to have seen a red apple on her coffee table an hour ago, as far as her perception goes, she saw the red apple; this much is true. The problem is: were there any molecules occupying the location of the image which had a causal effect or power that produced the image or sense datum?

I hope this has demonstrated the difficulty of discerning the difference between hallucination and reality, and how difficult it can be to convince someone otherwise. Has this made it any easier to work with a patient with regards to giving them some insight into their disorder? Or has it demonstrated the near impossibility of discerning the differences between hallucination vs reality? In some cases a psychotic patient might have hallucinations that are so far removed from reality that it might take medication and time to gain some insight into their illness. Or a patient might have hallucinations that are so close to reality such as olfactory or auditory hallucinations, it is extremely difficult to discern between the hallucination or reality.

I think one thing we can learn from this exercise in perception is to maybe find a simple way of explaining this theory of representative realism to the patient, and then challenge them to prove the existence of a causal object that produced the sense datum or image that they smelled, heard, or saw. Maybe based on this, they can gain some insight into the what they are seeing or hearing or smelling and it’s lack of correspondence to reality or the extended world.

This article on hallucination vs reality is not for diagnosing or treating any mental illness and strictly for informative purposes

Autor: Marie Gronley, MD

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