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 in itself 'Being in itself' to be at the same time the most vague and general concept possible to contemplate, but also the topic of greatest interest to him as a philosopher. In Sartrean existentialism, being-in-itself ("être-en-soi") is also contrasted with the being of persons, which he describes as a combination of, or vacillation or tension between, being-for-itself ("être-pour-soi") and being-for-others ("I'être-pour-autrui"). Being-in-itself refers to objects in the external world — a mode of existence that simply is. It is not conscious so it is neither active nor passive and harbors no potentiality for transcendence. This mode of being is relevant to