One of the absolutely central teachings of the Buddha is that of the three marks of existence. Along with the Four Noble Truths, the three marks form an integral part of the Buddhist understanding of the nature of reality. But the marks have been prone to misinterpretation, due in part to poor translations from the original Sanskrit in which they were written some two thousand years ago, but also from a philosophical standpoint. First, let's look briefly at just what the marks are.
The Buddha taught that everything that exists as a part of reality – objects, thoughts, ideas, people – has three essential properties which cannot be avoided. These properties, or marks, are: impermanence, suffering, and non-self.
Impermanence is probably the easiest to grasp, as it is the one which seems most obvious. Impermanence simply means that nothing lasts permanently. But even this is often misunderstood; impermanence not only means that nothing lasts forever – it is also a reference to the fact that nothing remains the same. In other words, everything is in constant flux, from one moment to the next. No two moments can possibly be the same. Everything in existence is undergoing a constant series of irrepressible changes. In short: there is no pause button to be found anywhere in the universe.
Exactly because nothing lasts forever and everything is undergoing continuous change, there is, too, an inherent unsatisfactoriness to everything in life – this is commonly translated from 'dukkha' as 'suffering', though it is more of a nod to the fact that nothing satisfies permanently. This of course is obvious when we consider the first mark of impermanence! However, the teaching of dukkha is what leads a lot of people to being turned off by Buddhism, coming to see it as pessimistic or even downright gloomy. Nothing could be further from the truth: far from wallowing, Buddhism promises to offer a way out of the endless cycle of suffering.
But the most misunderstood of the three marks of existence has to be 'non-self'. This states that everything lacks a separate self – that there is nothing in the universe, including you and I, which can be said to be possessive of a distinct 'self'. This, to many, seems like an outlandish claim. It seems as though the Buddha is denying all of human life! How can it be possible? Do I not exist? Well, the answer is yes and no. Let's look into this for a moment.
On the one hand, it would be absurd to say that you do not exist. Your body exists, your thoughts exist. However, the no-self philosophy states that there is nothing which can be said to be 'you', nothing which you possess which is separate from anything else. So it is not so much that you do not exist, but that you do not exist separately as a fixed thing. If you look deeply, you can see that everything which might be said to be you is in fact no more than an impersonal process, with any sense of ownership being ultimately illusory. You might feel, for example, that you are your body, or that it belongs to you, but that is absurd: if you cut off your toenail, is that still you? Is the air in your lungs you? Once you breathe out, is that same air you? Possibly not. You might associate the sense of self with the mind, the thoughts. But isn't the idea of 'me' just another thought, tacked onto other thoughts?
Does the self really exist? Does a library really exist, empirically? We know that the building exists, and the books inside it, but 'library' is no more than a label, is it? The same is true of the 'self'. The body exists, the thoughts exist, but the 'self' is just another label, is it not?
So, Buddhism is not really denying you at all; it's not all doom and gloom, and it's not obsessed with death. It does, however, passionately accept that the entire universe is under constant change – and that means you, too.