Why does Wittgenstein say in the Tractatus Logico-Philosophicus that the world has as its members only facts, not things? Focusing on this question, I start with the problem, in its general form, “How is it possible to determine something as X?” and establish the excluding-allowing model for determination. From this model, I derive an argument for Wittgenstein’s aforementioned statement. The argument shows that a whole cannot be determined as consisting of components that are determined separately in a strong sense, whereas in a weak sense it can be. This thus demonstrates why the context principle holds. The recommended interpretation places suitable weight on the Tractarian notion of possibility. It provides new insights into Wittgenstein’s conception of logic, and his atomism about facts and states of affairs.