Suppose I step into a room which is familiar to me but dark, and which has been rearranged [umgeräumt] during my absence so that everything which used to be at my right is now at my left. If I am to orient myself the 'mere feeling of the difference' between my two sides will be of no help at all as long as I fail to apprehend some definite object 'whose position', as Kant remarks casually, 'I have in mind'. But what does this signify except that whenever this happens I necessarily orient myself both in and from my being already alongside a world which is 'familiar'?1 The equipment-context of a world must have been presented to Dasein. That I am already in a world is no less constitutive for the possibility of orientation than is the feeling for right and left. While this state of Dasein's Being is an obvious one, we are not thereby justified in suppressing the ontologically constitutive role which it plays. Even Kant does not suppress it, any more than any other Interpretation of Dasein. Yet the fact that this is a state of which we constantly make use, does not exempt us from providing a suitable ontological explication, but rather demands one. The psychological Interpretation according to which the "I" has something 'in the memory' ["im Gedächtnis"] is at bottom a way of alluding to the existentially constitutive state ofBeing-in-the-world . Since Kant fails to  see this structure, he also fails to recognize all the interconnections which the Constitution of any possible orientation implies. Directedness with regard to right and left is based upon the essential directionality of Dasein in general, and this directionality in turn is essentially co-determined by Being-in-the-world. Even Kant, of course, has not taken orientation as a theme for Interpretation. He merely wants to show that every orientation requires a 'subjective principle'. Here 'subjective' is meant to signify that this principle is a priori.2 Nevertheless, the a priori character of directedness with regard to right and left is based upon the 'subjective' a priori of Being-in-the-world, which has nothing to do with any determinate character restricted beforehand to a worldless subject.
De-severance and directionality, as constitutive characteristics of Beingin, are determinative for Dasein's spatiality—for its being concernfully and circumspectively in space, in a space discovered and within-the-world. Only the explication we have just given for the spatiality of the ready-to-hand within-the-world and the spatiality of Being-in-the-world, will provide the prerequisites for working out the phenomenon of the world's spatiality and formulating the ontological problem of space.
1 '... in und aus einem je schon sein bei einer "bekannten" Welt.' The earlier editions have 'Sein' for 'sein'.
2 Here we follow the later editions in reading '... bedeuten wollen : a priori.' The earlier editions omit the colon, making the passage ambiguous.