Alfred North Whitehead occupies a place in the history of Western philosophy which makes his importance comparable only with that of the great masters - Plato, Kant and Hegel, who gave to mankind monumental systems of thought. Whitehead conceives the universe as an organism, a process, to understand which our notions of things, entities, substances, and of place and time have to be completely overhauled and transformed. We are generally accustomed to think that material bodies are located at particular points of space and instants in time, and that no other body can occupy those points of space at that time. This idea of what Whitehead calls 'simple location', which falsely tries to explain things without reference to other regions of space and time, is bound up with the common belief that causation is the production of an effect by a cause which precedes it in time. Whitehead's criticism is that a causal relation between two things is incompatible with their simple location, for two things which are separate from each other cannot bear a causally binding relation between themselves. Causation as it is ordinarily understood implies that a knowledge of the cause should give us the knowledge of all its effects. This is impossible if we persist in believing that things and events are separated from one another. If the simple location of events is a fact, even inference would give us no knowledge of the inferred events, for inference requires that the events from which we infer others should have an 'inherent reference' to the inferred events in order that they may give us knowledge of these latter; but such a reference is absent between events that are really different from each other. Memory of the past, too, would not be possible if all events are utterly cut off from one another in space and time. Our experiences oblige us to give up the belief in the simple location of things and events. There do not exist disconnected bodies or events at different points of space or moments in time.

If, then, events are not separated from one another, how can we distinguish between a cause and its effect, between the events from which we infer and those which we infer? Whitehead's answer is: By admitting a process that lies between all things, a process in which things themselves become parts of the process, a continuous flow of events, which takes us to the conception of the universe as an organism, a system in which every part influences every other part, every event is pervaded and interpenetrated by every other event. It is impossible to find anywhere in the universe isolated objects existing by themselves statically in space and time.

The theory of organism provides a solution to the problem of the relation between mind and matter. We are wont to think that mind and matter are two distinct facts of experience influencing each other in some way. But how can any mutual interference be possible if they are separated from each other? The problem can be solved only if mind and matter interact by a relation of process. Nature flows into the mind and flows out transformed by it into the objects of perception. Here, neither of the two is more real that the other. The perceiver and the perceived form one continuous process. There are no subjects and objects differentiated from one another. The perceived universe is a view of itself from the standpoint of its parts that are modified by the activity of its whole being. There is a continuity of process between mind and matter.

The relation of substance and its qualities, too, as it is generally understood, presents great difficulties. We cannot say how qualities inhere in a substance; we do not know whether they are different or identical. The usually accepted view is that substances are featureless things possessing only primary qualities, to which the secondary qualities are imparted by the knowing mind. Then there remains nothing in Nature except motion, which appears as light when it impinges on the retina and as sound when it strikes the eardrum. The world, says classical physics, consists of mere electrical charges, having no colour, no sound, no beauty, no good, no value, nothing that we call a world. The world is in our minds. What is real is electrical force, mathematical point-events, symbols and formulae. And what of aesthetic, ethical and religious values? Science has no such things as these. We also know how Locke's distinction of the primary qualities from the secondary ones led to the astonishing conclusions arrived at by Berkeley and Hume. Whitehead points out that classical science discovers a featureless universe because of the notion of simple location of things. It committed the mistake of abstracting things and events from their relation to others, and substances from the qualities which characterise them. The remedy is the acceptance of a universe of organic relations, where all facts, meanings and values are conserved without contradicting sense, reason and experience, and in which all spatial otherness and temporal distinction is overcome in a system of universal mutual reference of things and events. Space, time and events are organically related to each other; nothing can ever exist as isolated from other existences.

Whitehead learns from Hegel that all things and events are internally related and that to abstract them from their environment or their context in the whole would be to misrepresent them totally and to conceive them as what they are not. Matter is a group of agitations of force which extends its body to the entire universe and constitutes its stuff. The configurations of this force are called bodies or events and their existence and nature determine everything. Things are without limits or boundaries, they really exist everywhere, at every time, in every way. We cannot pluck a leaf from the tree and know what it is to the tree, or cut a part of the human body and know how it works as its organ. The bifurcation of an event from other events, of substance from its attributes, of cause from its effect, of mind from body, of things from the rest of the universe is a death-blow given to all right knowledge. Whitehead propounds a philosophy based on the scientific theory of relativity. The result is the novel concept of the organism.

Whitehead's universe as an organism is governed by the law of internal relations. All things are all other things in every condition, and the relations themselves are not independent of the things. Now, we have to give up the habit of using the words 'thing', 'entity', etc. while studying Whitehead, for he has pointed out that our ideas of thinghood are bound up with our notions of simple location involving what he calls the 'fallacy of misplaced concreteness'. What we call a thing is for him a set of agitations of force, a group of activity or energy, a configuration of process or motion, and he calls such a bit of process an 'actual occasion'. We shall, however, for the sake of convenience, apply this term to things in general or objects of our experience. Sometimes, Whitehead calls these actual occasions 'drops of experience'. These names given to the material of the objects of common perception are to bring out that they are not isolated entities but currents of teleological process, continuous with all things in the universe. No part of the process can be abstracted from the others and studied correctly. Every actual occasion involves every other, and to know any one is to know the whole universe. Actual occasions are spatio-temporal aspects of process, a nexus of which we call an object. An object is nothing but a continuous process of actual occasions as we experience them in their externalised condition. There is no fixed object anywhere. An event is a series of actual occasions revealed in perception as demonstrated in a molecule for a few moments. Objects are more complex formulations of such events. The objectness of an object is in its capacity to be experienced in perception.

Every actual occasion is sensitive to the existence of others, and thus to the entire universe. All actual occasions take account of each other, and in some way, subtler than even sense-perception, 'perceive' each other. There is a kind of pervasive 'feeling' of every actual occasion for the others in the universe. Whitehead uses the word 'feeling' in quite a different sense from the one in which we are used to understand it, and makes it more fundamental than the conscious level of the mind in waking life. This feeling is a natural sympathy which the actual occasions have for the whole, a general connectedness and unity of the universe which they reveal in themselves by the very fact of their constitution. This rudimentary feeling or experience is, to Whitehead, of the nature of unconscious 'prehension' or taking into relation of the other actual occasions, a grasping of the characteristics of every aspect of the universe. The prehensions may be positive absorbings or negative rejections of aspects. The actual occasions are thus related both in physical and mental life; the two are not features of distinct orders of being. The process is feeling and reality, and the energy of physics is but what we feel within ourselves as minds, a feeling in our own constitutions as actual occasions for the indivisible process which is the universe. Every actual occasion represents and feels a situation of the entire process, and its very existence is due to the contribution of the rest of the actual occasions; it is produced by the whole universe by way of integration of characters, which Whitehead calls the process of 'concrescence'. An actual occasion is called more precisely a 'prehensive occasion', for it has no existence independent of its prehensions.