Our common phylogenetic endowment enables us to communicate with other humans and some higher animals through sounds or gestures. We also have the abstract capacity to develop a complex symbolic language, but language acquires meaning only when grounded in qualitative experiences. Language can name ineffable experiences, but we cannot transfer their meaning through explanations. Thus, language is incomplete because it is not a closed circular system, and needs to be grounded in independent intuitions, as mathematics does. Propositional knowledge is generally considered the "highest" form of knowledge, which allows us to construct our cultural universe and the world of values in which we live. The consistency of science and our capacity to interact successfully with the world illustrate the usefulness and reliability of our intuitions, language, and knowledge.