Once it is admitted that reality exists independently of the mind, and that it is not absurd, a new requirement immediately imposes itself: reality must be intelligible through distinctions.

To understand is never to grasp an indistinct whole. To understand is to distinguish without separating. Where there is no real distinction, there is nothing to understand—only a confused mass, or worse, a pseudo-whole verbally affirmed but conceptually empty.

Realist philosophy therefore affirms a simple but explosive principle for much modern thought:

What is, is composed of really distinct principles.

Caution: this is not about mere distinctions of language, nor arbitrary divisions of the mind. It is about distinctions grounded in the very being of things. Reality is not a homogeneous paste on which the mind would trace artificial boundaries; it is structured from within.

To refuse this is to condemn all serious intelligibility.

Why distinction is ontologically necessary

To say that a thing is intelligible is to say that it can be thought as something determined. Yet all determination presupposes a distinction: to be this rather than that, to be in such a way rather than another.

If everything were absolutely simple, in the sense of undifferentiated, then:

• nothing could be attributed to anything,
• no property could be distinguished from that to which it belongs,
• nothing could be said to be "the same" or "other."

In other words: without real distinctions, there are no beings, only an empty word: "the whole."

Modern thought sometimes likes to invoke this indeterminate, fluid "whole" without proper structure, to escape metaphysical difficulties. But this is not a solution; it is an evasion. For a "whole" without distinctions is not a real whole; it is a poorly named nothingness.

Some fundamental distinctions

At this stage, it suffices to recognize that certain distinctions are unavoidable, even to think the most ordinary things:

• distinguishing a thing from what it is not;
• distinguishing what a thing is from what it does;
• distinguishing what remains from what changes;
• distinguishing what belongs to a thing from what happens to it.

These distinctions are not refinements of idle philosophers. They are already at work in our most elementary way of speaking, acting, and understanding. The philosopher does not invent them; he makes them explicit.

Down to earth: without distinction, nothing is thinkable

Let us take things simply, once again.

First example: an ordinary object. A cup is white, placed on a table, hot. The whiteness is not the cup. The heat is not the cup. And yet, they do not float in a void: they belong to something. If I do not distinguish the cup from its properties, I can no longer say anything about it. Either everything is the cup, or nothing is.

Second example: change. A leaf is green, then it turns yellow. If I do not distinguish what remains (the leaf) from what changes (its color), then change becomes impossible to think. The leaf would be destroyed at every instant, replaced by another. Yet we know this is not the case.

Third example: mistaken identification. I think I see someone, then realize I was wrong. This correction presupposes that I distinguish between the thing as it is and the way it appears to me. Without distinction between reality and my relation to reality, error would make no sense.

Fourth example: action. When someone acts, we spontaneously distinguish the agent and the act. To do is not to be, even if the act reveals what someone is. Confusing the two leads either to denying responsibility or to freezing being in the instant.

In all these cases, the same lesson returns: without real distinctions, the world becomes unintelligible.

An immediate consequence (often refused)

To recognize real distinctions is already to refuse two very modern temptations:

• crude monism, which reduces everything to a single undifferentiated reality;
• nominalism, which makes distinctions mere linguistic conventions without ontological foundation.

In both cases, one obtains a discourse that speaks much but no longer accounts for anything.

Realism, on the contrary, affirms that our distinctions are not arbitrary when they are correct: they correspond to something in reality. They can be refined, corrected, deepened—but they are not illusory.

At this stage, one distinction will become absolutely central for what follows, because it conditions the very possibility of change without contradiction: the distinction between what is in potency and what is in act.

It is this distinction that will allow us to understand how something can become other without ceasing to be what it is.

And it is from this distinction that metaphysics will definitively cease to be a conceptual game and become a necessity.