  But what exactly would one do in order to safeguard the fourfold in its essential unfolding. Recall that in Building Dwelling Thinking Heidegger presents safeguarding as a four-dimensional way of Being. The first two dimensions—saving the earth and receiving the sky as sky—refer to our relationship with the non-human natural world. As such they forge a genuine connection between the later Heidegger and contemporary environmentalist thinking. However, the connection needs to be stated with care. Once again the concept of poiesis is central. Heidegger holds that the self-organized unfolding of the natural world, the unaided blossoming of nature, is itself a process of poiesis. Indeed it is poiesis “in the highest sense” (Question Concerning Technology 317). One might think, then, that saving the earth, safeguarding in its first dimension, is a matter of leaving nature to its own devices, of actively ensuring that the conditions obtain for unaided natural poiesis. However, for Heidegger, saving the earth is primarily an ontological, rather than an ecological, project. ‘Save’ here means “to set something free into its own essence” (Building Dwelling Thinking, p.352), and thus joins a cluster of related concepts that includes dwelling and also poiesis as realized in artisanship and art. So while, say, fiercely guarding the integrity of wilderness areas may be one route to safeguarding, saving the earth may also be achieved through the kind of artisanship and its associated gathering of natural materials that is characteristic of the traditional cabinetmaker. The concept of saving as a setting free of something into its own essence also clears a path to another important point. All four dimensions of safeguarding have at their root the notion of staying with things, of letting things be in their essence through cultivation or construction. Heidegger describes such staying with things as “the only way in which the fourfold stay within the fourfold [i.e., safeguarding] is accomplished at any time in simple unity” (Building Dwelling Thinking 353). It is thus the unifying existential structure of safeguarding.