Kant's monumental Critique of Pure Reason (1781/1787) begins with his account of perception. Look around you. An experience is the result. You seem to see a chair and a person, say – your spouse at rest. A welcome sight. A gift from the world, in more than one sense. Yet not all aspects of the experience – even perhaps of its content – are coming to you from the world, according to Kant. What else is involved? An intuition of space (says Kant). An intuition of time, too.Footnote ¹ It is not that you observe your spouse and your chair, before adding to these parts of your experience your intuitions of space and of time. Rather, you observe your spouse and your chair at all, partly by enveloping within those intuitions of space and of time whatever sensory matter the world is giving you at that moment. In this way, your perceptual experiences have a recurring spatio-temporal form or structure, within which differing details from the outer world are given an informative role. There is no other way for you to have an observational experience. You already have intuitions of space and of time, prior to having any sensory interactions with the world; and only by having those intuitions are you able to experience those sensory interactions as observations.

That is a familiar tale, adapted from one of philosophy's greatest talers. It is also a transcendental tale, claiming to describe essential and universal preconditions for anyone's having any experiences of the world. And we may well infer that empirical testing of the Kantian story is therefore beside the point. Of course, it is also possible that part of our reason for thinking of a transcendental tale as the only means we have of evaluating this issue is our presuming that no empirical test is available. After all, if Kant is right then we cannot have a sensory experience from which our intuitions of space and of time are absent. At any rate, we cannot actually divest ourselves of the latter intuitions, in order to ascertain directly what difference this makes to our observational experiences.

Or so we may well believe. But in fact this is possible. Maybe not deliberately so, with prior intent and planning; nevertheless, the same outcome is attainable. I have had such experiences. I still do. Here is my own Kantian report.

Every so often, I experience transient global amnesia (TGA).Footnote ² I ‘black out’, either collapsing or leaning limply against something solid such as a wall.Footnote ³ After I reopen my eyes, there is a period of time – not long; real, though – during which I see the world without really seeing it. I gaze at a chair or at my wife, perchance. And although – as, only afterwards, I might describe it – I am having an experience containing the relevant shapes and colours, I do not really see a chair as such or my wife as such. What else is missing? The dominant feature of that time is my having no sense of time – none at all. Notably, I have no sense of my having a past, indeed of anything's having one, or even of there being one available in the world. This blankness is accompanied by my not seeing the person in front of me as a person, let alone as my wife. Nor do I see spatial depth. I have no sense of the possibility of examining an observed object from further angles, for instance. The chair, seen superficially, conveys to me no sense of its function, of its nature.

Then gradually – but through no effort of will on my part (I have no sense of a will, an ability to choose, within me at that time) – I begin to regain what I had lost. My past is restored to me – a sense of some past, and then of its specific details. I feel this happening, unfolding. And as it happens, so too I start seeing my surroundings anew. Content returns – the sort of content we would otherwise take for granted as available in any sensory experience. Slowly, an object, a thing, a coloured expanse, becomes once more my wife – or even a woman at all. The chair will again seem solid and available – a chair as such. An external environment thus takes shape, gains hue and heft; and the only other change that seems to be allowing this to occur is the returning to me of the intuitions of space and of time. As these – especially the intuition of time, it seems – return, it is as if something comes to be some thing, then more than a mere thing in the world, and finally a thing with personal resonance. It is as if objects thicken and come alive (or as alive as some of them can be). In that way, whatever I am seeing will now, only now and seemingly only for that reason, mean something to me – emotionally, of course; but even as part of a world at all and part of a life that is mine within that world. In one respect, there is no personal advance in this: what I am now seeing will mean only what – if not for the TGA – it would never not have meant. Once more I am me, with a past and a location. Once more, what is around me has a past and a location. All of this, however, only once the intuitions of space and of time are returned to me.

What do such experiences suggest about the nature of perception? I infer from them a Kantian moral.Footnote ⁴ I regard these experiences as providing a means, one that is generally unavailable in practice to people, of actually having experiences from which the enveloping intuitions of space and of time are absent – and of these experiences, as a result, not being genuinely observational. To have such experiences is to ‘live’ some empirical evidence in favour of what otherwise could only strike us as an abstract philosophical argument on Kant's part.

For the TGA, I believe, robs me of my general intuitions of space and of time – apparently parts of my means of ever observing the world as a world at all. Until these find their way back to me, I do not really observe the world. A chair is not a chair for me until that happens. My wife – yes, even she – is not a person for me during those moments. (I am also neither I nor me. I am lost from myself. As time disappears, so do I. But this is another aspect of the story. In this paper my focus is only upon my experiences of the outer world.)

I do not panic when caught by the TGA. How could I? At that time, I have in mind no alternative ways for me to be. Afterwards, though, once the TGA has passed away, naturally I revisit, recollect, reflect. Then I am perturbed – for a while – at where I have been; yet relieved also at no longer being there.

Then, too, I think of Kant. And I wonder whether he ever experienced TGA. I would not be surprised to be informed that he did.Footnote ⁵