A dream need not always involve pictures. I have had dreams about philosophy without any images at all. I work in metaphysics, that most abstract area of philosophy. What interests me is how in general terms the world fits together and works. Is it composed of particulars, properties, events, laws, facts and so on? Because these ideas are so abstract they cannot be visualised, so it has come as a pleasant surprise to me that during my most intense periods of thought I am able to dream about metaphysics.

Such a dream gave me the first eureka moment of my career, which I now think of as my intellectual breakthrough. The problem I had been working on concerned what philosophers call dispositional properties. Commonplace examples are fragility, solubility, elasticity and flammability. These are properties that seem capable of manifesting themselves in certain events or changes, such as when a sugar cube dissolves or a flammable substance burns.

Some call such dispositions powers and I am happy to use the terms disposition and power interchangeably. When I read in my postgraduate days the existing literature on the subject, which was hardly voluminous, philosophers spoke also of there being another kind of property in the world. They said that properties such as shape - being round, square, spherical and so on - were non-dispositional. These were called categorical properties. There were other distinctions and contrasts in the offing, however, and I found the whole discussion somewhat confusing.

I started working on dispositions for my PhD, but my advisers were rather sceptical of the project. There had been some work on the subject in the 1930s, but I was told that the Harvard University philosopher Willard Van Orman Quine had solved all the problems in the 1960s. I had a PhD upgrade examination at which my professors gave me a tough time and tried to persuade me to move on to something more productive. The subject was out of fashion and, they tried to tell me, virtually dead.

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Discouraged, I went on holiday in August 1992 to the island of Guernsey, and it was there that I had my first dream about metaphysics. The problems and concepts shifted around in my mind, each alternative solution coming before me and then fading away. But then I was presented with a solution that would work - identity - and I awoke shortly afterwards and said aloud to myself: "It's identity!"

The basic idea was that the world was not divided into two different kinds of property after all. Indeed, no one had ever convincingly distinguished dispositional and categorical properties. The thought was that they were one and the same.

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Consider a paradigmatic categorical property such as being spherical. Anything that has this property also has the disposition to roll in a straight line down an inclined plane. It may also have other dispositions, such as the power to leave a smooth hollow if pressed into a soft cushion. Of course, a sticky soap bubble is spherical and may not roll down an inclined plane, but it is nevertheless still disposed to do so: it is merely that this disposition is counteracted by other dispositions - floatiness and stickiness.

The eureka idea I had was that dispositional and categorical properties were one and the same thing, just thought of in different ways. So to be spherical was nothing more nor less than to have a bundle of dispositions or powers, such as to roll down an inclined plane, leave a hollow in a soft cushion, and so on. And, as I thought about it, I decided that this could be true of all properties. They were all, either overtly or covertly, bundles of dispositions or powers.

I am not denying that others have had this insight, nor that there was still much work to be done to develop it to a point where my peers would take it seriously. But I stuck with the idea, which then formed the basis of my PhD thesis and eventually my first book, Dispositions (1998). When it came out, I was shy about it and rather hoped no one would read it. But it was read, reviewed and well received. More than that, it seemed to revive what had been a moribund subject.

For the first time, international conferences were organised on dispositions, to which I was invited as a (reticent) authority figure. Suddenly, everyone seemed interested in dispositions and now, 12 years after my first book was published, the journals are full of papers on the subject. I remember how virtually no one took dispositions seriously back in 1992, usually doubting that they even existed. But now the tables have turned and younger graduate students sometimes ask me how anyone could not have believed that our world is a world of powers.

But what does all of this matter, other than to the career of an obscure metaphysician? What is the point of it all? It so happens that the question of dispositions matters a lot, especially with regard to explanations of how the world works. To see why, I will need to explain my second eureka moment, because I have had two in my career so far.

We need to fast-forward to 2003 when, in a period of study leave, I was contracted to write a book on the laws of nature. I had been thinking about this since finishing Dispositions and my initial idea was merely to emphasise that laws should be interpreted as having dispositional force only: they are not absolute, but are about what tends to happen.

If we take the law of gravitational attraction, for instance, we see that apples tend to fall to the ground, but they need not do so always if, for instance, they are picked by a safe hand or a hurricane whisks them away. The so-called laws of nature should not be thought of as strict, therefore, because they all seem to admit exceptions.

My second eureka moment was not as romantic an episode as a dream worked out by my subconscious: it was more perspiration than inspiration. I had a large old-fashioned blackboard in my office back then and it was covered with scribblings in chalk. I had plotted out a mental map with all the key concepts and the connections between them. I was searching for a sensible stance to take on laws and locked myself in my room for long periods when everyone else seemed to be out having a good time.

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At one moment it suddenly struck me that the common idea that the world is governed by inviolable laws of nature was not true at all. It wasn't just that there were no exceptionless laws, but rather that there were no laws at all. If all properties were dispositional in character, they could do their work unaided by any law. Indeed, the laws of nature seemed superfluous.

Why should we accept such a view? Laws of nature and the role they play traditionally have been understood in two ways. The first way we can call descriptivist. This is just the view that the laws are descriptions of the relatively stable and uniform regularities that happen to occur. But laws, under this interpretation, are not really a separate category of things that do any work. They are descriptions of something else, and it may be that powers or dispositions drive any regularities that can be found. Descriptivism does not really vindicate laws as existents.

The second way to understand laws is prescriptivist. This is the idea that laws prescribe or govern the regularities of the world. This is a popular and common view and it can be found, for instance, in Cassell's Laws of Nature by James S. Trefil (2002), a reference work that attempts to set out what all the laws are. But, I started to wonder, how could laws do such things? What could they be in the world for them to be capable of governing the movements and changes of things, so that they must behave in accordance with them?

In the legal and moral cases, a law can be enforced and a system of sanctions put in place for those who break it. But nature has no sanction against my breaking its laws. Of course, it needs no such sanction in any case, as it seems a matter of impossibility that I violate any such natural law.

I tried to turn on its head this whole lawful way of thinking: of the world being governed by these things called the laws of nature. I thought of natural law as a metaphysically misleading metaphor. If all properties were dispositions, then the objects and substances that had such properties would not need governing by anything outside themselves. Sugar tends to dissolve, for instance, not because there is an external law of nature that makes it do so, but because it has a dispositional property to dissolve.

There is a counterargument, which I think is misguided, that without the addition of some extra governing law, nature would be chaotic: while some sugar cubes would dissolve, others would burst into flames and others grow wings and fly. But this is never a possibility and things will behave in a more or less regular way even without laws. What makes something the property it is, from the dispositionalist view, is how it is disposed to behave. And furthermore, what makes something the kind of substance or thing that it is rests entirely on the dispositional properties it bears. Hence, all sugar will be soluble because it would not be sugar if it were not. Similarly, for the case of gravitational attraction, all masses attract all other masses, in exactly the proportion indicated by the gravitation law, because that is what it is to have mass. Hence, anything that did not attract other masses would not itself be a mass.

I wrote down these ideas in my book Laws in Nature (2004), which in my view is a better and more significant book than Dispositions, although I don't feel it has had quite as big an impact. The main thesis, that there are no laws of nature in the world, is perhaps thought to be a step too far. After all, I was looking to overturn what many consider to be one of science's sacred ideas, dating back at least to Isaac Newton, of a law-governed universe.

But I was not challenging anything that scientists do in practice. I don't think science ever bothers directly with the metaphysical questions of how the world works. Scientists can go on discovering the robust regularities of the world and leave it to the metaphysicians to consider how, if at all, such regularities are produced.

But who is to say what would come from such a lawless view of the world if it were adopted? Philosophical ideas can take decades or centuries to affect wider thinking, but I would certainly argue that they do. Science and society often take their inspiration from thinking of a more abstract kind that eventually has a concrete impact on our lives.

Thus far in my career I have had two eureka moments, but I hope to have at least a few more. During heavy periods of research, I've had other metaphysical dreams. I am always happy when I do, especially since I rarely have any dreams at all, and always think carefully upon waking to see whether my mind's free association has delivered me any fortuitous new insights.

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