From William James, A Pluralistic Universe

Pragmatically interpreted, pluralism or the doctrine that it is many means only that the sundry parts of reality may be externally related. Everything you can think of, however vast or inclusive, has on the pluralistic view a genuinely ‘external’ environment of some sort or amount. Things are ‘with’ one another in many ways, but nothing includes everything, or dominates over everything. The word ‘and’ trails along after every sentence. Something always escapes. "Ever not quite’ has to be said of the best attempts made anywhere in the universe at attaining all-inclusiveness. The pluralistic world is thus more like a federal republic than like an empire or a kingdom. However much may be collected, however much may report itself as present at any effective centre of consciousness or action, something else is self-governed and absent and unreduced to unity.

Monism, on the other hand, insists that when you come down to reality as such, to the reality of realities, everything is present to everything else in one vast instantaneous co-implicated completeness–nothing can in any sense, functional or substantial, be really absent from anything else, all things interpenetrate and telescope together in the great total conflux.

For pluralism, all that we are required to admit as the constitution of reality is what we ourselves find empirically realized in every minimum of finite life. Briefly it is this, that nothing real is absolutely simple, that every smallest bit of experience is a multum in parvo plurally related, that each relation is one aspect, character, or function, way of its being taken, or way of its taking something else; and that a bit of reality when actively engaged in one of these relations simultaneously. The relations are not all what the French call solidaires with one another. Without losing its identity a thing can either take up or drop another thing, like the log I spoke of, which by taking up new carriers and dropping old ones can travel anywhere with a light escort.

For monism, on the contrary, everything, whether we realize it or not, drags the whole universe along with itself and drops nothing. The log starts and arrives with all its carriers supporting it. If a thing were once disconnected, it could never be connected again, according to monism. The pragmatic difference between the two systems is thus a definite one. It is just thus, that if a is once out of sight of b or out of touch with it, or, more briefly, ‘out’ of it at all, then, according to monism, it must always remain so, they can never get together; whereas pluralism admits that on another occasion they may work together, or in some way be connected again. Monism allows for no such things as ‘other occasions’ in reality–in real or absolute reality, that is.

The difference I try to describe amounts, you see, to nothing more than the difference between what I formerly called the each-form and the all-form of reality. Pluralism lets things really exist in the each-form or distributively. Monism thinks that the all-form or collective-unit form is the only form that is rational. The all-form allows of no taking up and dropping of connexions, for in the all the parts are essentially and eternally co-implicated. In the each-form, on the contrary, a thing may be connected by intermediary things, with a thing with which it has no immediate or essential connexion. It is thus at all times in many possible connexions, which are not necessarily actualized at the moment. They depend on which actual path of intermediation it may functionally strike into: the word ‘or’ names a genuine reality. Thus, as I speak here, I may look ahead or to the right or to the left, and in either case the intervening space and air and aether enable me to see the faces of a different portion of this audience. My being here is independent of any one set of these faces.