Existentiell and existential are key terms in Martin Heidegger's early philosophy. Existentiell refers to the aspects of the world which are identifiable as particular delimited questions or issues, whereas existential refers to Being as such, which permeates all things, so to speak, and can not be delimited in such a way as to be susceptible to factual knowledge. In general it can be said that "existentiell" refers to a "what", a materially describable reality, whereas "existential" refers to structures inherent in any possible world. In other words, the term "existentiell" refers to an ontic determination, whereas "existential" refers to an ontological determination.