The upshot of this is that if in our analysis of dealings we aim at that which is dealt with, then one’s existent Being alongside the entities with which one concerns oneself must be given an orientation not towards some isolated item of equipment which is ready-to-hand, but towards the equipmental totality. This way of taking what is dealt with, is forced upon us also if we consider that character of Being which belongs distinctively to equipment that is ready-to-hand—namely, involvement.xvii We understand the term “involvement” ontologically. The kind of talk in which we say that something has with it an involvement in something, is not meant to establish a fact ontically, but rather to indicate the kind of Being that belongs to what is ready-to-hand. The relational character of involvement—of its ‘with… in…’—suggests that “an” equipment is ontologically impossible. Of course just a solitary item of equipment may be ready-to-hand while another is missing. But this makes known to us that the very thing that is ready-to-hand belongs to something else. Our concernful dealings can let what is ready-to-hand be encountered circumspectively only if in these dealings we already understand something like the involvement which something has in something. The Being-alongside which discovers circumspectively in concern, amounts to letting something be involved—that is, to projecting an involvement understandingly. Letting things be involved makes up the existential structure of concern. But concern, as Being alongside something, belongs to the essential constitution of care; and care, in turn, is grounded in temporality. If all this is so, then the existential condition of the possibility of letting things be involved must be sought in a mode of the temporalizing of temporality.
Heidegger: ontological meaning of "involvement" || Return to the claim that "'an' equipment is ontologically impossible"