We think sleep is one of the most fundamental acts of self - care. (mindbodygreen.com)
In Aristotle, the form is the purest, most fundamental act; but Aristotle is not to be automatically equated with Thomas, who held that the act of Being is more primordial than that of the form, a distinction which preserves his metaphysics from the pitfalls of Aristotelian essentialism. (faith.org.uk)
In this deeper sense, «to be» is the primitive and fundamental act by virtue of which a certain being actually is, or exists -LRB-...) «to be» is the very act whereby an essence is.» (faith.org.uk)