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of the 'world' will provide us likewise with a negative support for a positive explication of the spatiality of the environment and of Dasein itself. With regard to Descartes' ontology there are three topics which we shall treat: 1. the definition of the 'world' as res extensa (Section 19); 2. the foundations of this ontological definition (Section 20); 3. a hermeneutical discussion of the Cartesian ontology of the 'world' (Section 21). The considerations which follow will not have been grounded in full detail until the 'cogito sum' has been phenomenologically destroyed. (See Part Two, Division 2.)1

19. The Definition of the ' World' as res extensa.

Descartes distinguishes the 'ego cogito' from the 'res corporea'. This distinction will thereafter be determinative ontologically for the distinction between 'Nature' and 'spirit'. No matter with how many variations of content the opposition between 'Nature' and 'spirit' may get set up ontically, its ontological foundations, and indeed the very poles of this opposition, remain unclarified; this unclarity has its proximate [nachste] roots in Descartes' distinction. What kind of understanding of Being does he have when he defines the Being of these entities? The term for the Being of an entity that is in itself, is "substantia". Sometimes this expression means the Being of an entity as substance, substantialiry; at other times [90] it means the entity itself, a substance. That "substantia" is used in these two ways is not accidental; this already holds for the ancient conception of οὐσία.

To determine the nature of the res corporea ontologically, we must explicate the substance of this entity as a substance—that is, its substantiality. What makes up the authentic Being-in-itself [An-ihm-selbst-sein] of the res corporea? How is it at all possible to grasp a substance as such, that is, to grasp its substantiality? "Et quidem ex quolibet attributo substantia cognoscitur; sed una tamen est cuiusque substantiae praecipua proprietas, quae ipsius naturam essentiamque constituit, et ad quam aliae omnes rejeruntur."iii Substances become accessible in their 'attributes', and every substance has some distinctive property from which the essence of the substantiality of that definite substance can be read off. Which property is this in the case of the res corporea? "Nempe extensio in longum, latum et profundum, substantiae corporeae naturam constituit."iv Extension—namely, in length, breadth, and thickness—makes up the real Being of that corporeal substance which we call the 'world'. What gives the extensio this distinctive status? "Nam omne aliud quod corpori tribui potest, extensionem praesupponit ..."v Extension is a state-of-Being constitutive for the entity we are talking about; it is that

1 This portion of Being and Time has never been published.

Being and Time (M&R) by Martin Heidegger