Rational Existence is a simple idea that goes to the foundation of all thought and all explanation. Acceptance of Rational Existence is acceptance that the basis of humanity is rational and further that our rationality has existence. Proof of Rational Existence is tautology: RE is the idea that ideas have a rational existence. It is not possible to aknowledge the existence of any word or thought without acknowledging RE.
If a tree falls in the woods it makes no difference if there are no beings in the universe which understand what trees are, what falling is, and where the woods are. The importance of existence are ideas that allow explanation, conceptuality, intellectualization. The acceptance of the existence of ideas is Rational Existence. A REt confirms and reifies the existence of a tree, of falling, and of woods. Existence is a concept, and without concepts there can be no notion of existence, hence the tautology.
The importance of RE is most apparent in religion. All religion requires the acceptance of an unknowable or at the very least unprovable hypothesis. Once RE is accepted, however, one is faced with defining the structure and not the substance of the unknowable. God, therefore, or Jesus, or Muhammad or the Buddha can no longer be viewed as physical beings, whether or not they ever were, indeed no being or animal or rock or atom is viewed as merely physical because every recognized entity has a part in rational existence. Nothing meaningful can be merely physical because its very recognition puts it in relationship with concepts, models and ideas which have a greater existence than the physical.
Much of what is unknown must have the very same structure as the known, whether or not we know that structure. We cannot know substance, but only relationships, aspects and attributes of the structure of some things. RE acknowledges that the importance of existence is not physical, but rather the relationships, aspects and attributes of what exists physically. The idea, the structure, the concept, the relationships, aspects and attributes are the important existence while the physical objects we relate to have only tangential existence.
Allowing for the existence of concepts need not force the creation of metaphysics, platonic forms, a spirit world, humors or magic. We need not define existence or separate existence from physicality. Acknowledging that our existence is conceptual goes a long way toward reconciling religion and science as well as forming a foundation for psychology and learning theory.