Love, like axioms, can not be demonstrated.

We do everything by custom, even believe by it; our very axioms, let us boast of our Freethinking as we may, are oftenest simply such beliefs as we have never heard questioned. [ Carlyle ]

Not only the individual experience slowly acquired, but the accumulated experience of the race, organized in language, condensed in instruments and axioms, and in what may be called the inherited intuitions - these form the multiple unity which is expressed in the abstract term experience. [ G. H. Lewes ]