Being and Time Heidegger's "description of the world of phenomena" to be "fascinating, but maddeningly abstract". He suggests that much of "Being and Time" is a "description of a private spiritual journey" rather than genuine philosophy, and notes that Heidegger's assertions are unsupported by argument. Stephen Houlgate compares Heidegger's achievements in "Being and Time" to those of Kant in the "Critique of Pure Reason" (1781) and Hegel in "The Phenomenology of Spirit" (1807) and "Science of Logic" (1812-1816). Simon Critchley calls the work Heidegger's "magnum opus", and writes that it is impossible to understand developments in continental philosophy after Heidegger without understanding it.
Being and Time of what a hammer "is" is not determined by a theoretical understanding of its presence, but by the fact that it is something we need at the moment we wish to do hammering. Only a "later" understanding might come to contemplate a hammer "as" an object. The total understanding of being results from an explication of the implicit knowledge of being that inheres in "Dasein". Philosophy thus becomes a form of interpretation, but since there is no external reference point outside being from which to begin this interpretation, the question becomes to know in which way to proceed with this