Threshold threshold, the strip or line that marks the boundary between one space and another—between outside and inside, between one room and the next—is both a physical feature and a potent symbol. One crosses a threshold when one enters a building, a stage of life, or a new condition. The threshold is thus a limit that is also a passage: it divides, but it is precisely at the threshold that transition occurs. To stand on the threshold is to be neither fully here nor fully there—to be in a state of betweenness that has been associated with ritual, with danger, and with the possibility of transformation. In architecture and custom, the threshold has often been charged with significance. In many traditions, one does not simply step over it; one is welcomed across it, or one pauses to acknowledge the transition. The threshold marks the boundary between the public and the private, the profane and the sacred, the familiar and the unknown. To cross it is to accept a change of status—guest, initiate, bride. The physical threshold thus becomes the site of rites of passage, and the act of crossing is invested with meaning that exceeds the mere change of location. The limit here is not only spatial but symbolic: it is the point at which one kind of order gives way to another. In narrative and drama, the threshold often appears as the moment of decision or the point of no return. The hero stands at the threshold of the underworld, the cave, or the unknown; to cross is to commit to a journey from which return may be difficult or impossible. The threshold is thus the limit of the ordinary world—the edge beyond which the rules may change. This narrative function of the threshold reflects a deeper theme: that limits are not only boundaries but points of transition, and that the most significant limits are those at which something is risked or gained. In philosophy, the concept of a threshold can be used to model the idea of a critical point—a value or a condition at which a qualitative change occurs. Below the threshold, a system behaves one way; above it, another. The threshold is the limit that separates two regimes. This usage is common in the natural and social sciences (threshold effects, threshold concepts), but it has a philosophical analogue in the idea of a limit at which our concepts or our obligations shift. Is there a threshold of harm below which we have no duty to act? A threshold of evidence above which we are justified in believing? The metaphor of the threshold suggests that such boundaries are sharp, but in practice we may find only gradients and grey zones. The threshold then becomes an idealisation—a way of representing a transition that in reality may be spread over a range. The threshold is also an image for the limit of consciousness or of expression. We speak of the threshold of perception—the minimum stimulus that can be detected—and of the threshold of pain. We speak of being at the threshold of understanding, or of what can be said. In these uses, the threshold is the boundary between the manifest and the latent, the sayable and the unsayable. To approach the threshold is to approach a limit of our capacities; to cross it may be to enter a domain that we cannot fully articulate or that we experience only as intensity or confusion. In the context of limits and boundaries that concern this volume, the threshold reminds us that limits are not only barriers but points of passage. The limit is not only what we cannot cross but what we cross when we change. That duality—limit as barrier and limit as passage—is essential to the threshold. It is why the image has retained its power across cultures and disciplines: it captures the ambiguity of the boundary as both separation and connection, both end and beginning. [role=marginalia, type=objection, author="Reviewer", status="adjunct", year="2026", length="42", targets="entry:threshold", scope="local"] I remain unconvinced that the threshold can be so easily reduced to mere boundaries and transitions. From where I stand, its complexity lies in the psychological and cognitive processes that it activates, which are far more intricate than merely marking divisions. This account risks overlooking the bounded rationality of individuals as they navigate these liminal spaces, often experiencing them as more than just physical passages but as sites of profound decision-making and reflection. See Also See "Limits" See "Infinity"