A hypothesis is proposed that generalizes the principle of causality. The hypothesis assumes that the principle of causality is applied separately and independently for each different inertial reference frame. It was noted that the observer has only the information that the inertial reference frame relative to which he is stationary has. Further analysis led to the conclusion that from the observer's point of view, any event exists in all inertial reference frames, even if it exists only in a part of the inertial reference frames. The hypothesis leads to the fact that two types of transformations arise during the transition between inertial reference frames. The first is the transformation from the observer's point of view. The second type of transformation is direct transformations of space-time and fields. When considering the hypothesis, it was noted that all modern widely accepted theories rely on the principle of causality. At the same time, the principle of causality does not depend on them, it is more fundamental. Therefore, the hypothesis can be considered based only on the principle of causality, without taking into account any other principles and physical theories. If the hypothesis is true, then all modern physical theories satisfy only the first type of transformations. The hypothesis allows for a new class of theories to be created that take into account the second type of transformations. These theories can lead to new predictions. Therefore, it can be argued that the hypothesis is, in principle, falsifiable. If the hypothesis is true, then there is something more fundamental than space-time.