A niche in meaning space insists on being filled if possible, and determines the form of its occupant, but not the actual existence of that occupant. It can only select something more or less vaguely resembling that form and actually existing in the universe where the system can find it; the act of meaning, the triadic action of a sign, involves its existence, its secondness.
There are different kinds of existence. There is the existence of physical actions, there is the existence of psychical volitions, there is the existence of all time, there is the existence of the present, there is the existence of material things, there is the existence of the creations of one of Shakespeare’s plays, and, for aught we know, there may be another creation with a space and time of its own in which things may exist. Each kind of existence consists in having a place among the total collection of such a universe. It consists in being a second to any object in such universe taken as first. It is not time and space which produce this character. It is rather this character which for its realization calls for something like time and space.
— Peirce, CP 1.433 (c. 1896)
In this sense, Secondness as individual existence ‘calls for’ continuity as Thirdness, while on the other side of the coin of meaning, the niche in meaning space ‘calls for’ its inhabitation. Semiosic determination, like the ‘imprinting’ of a new hatchling on its parent, is a reciprocal realization.
We know that the newborn chick looking for its mom actually relies on at least two different neural systems, one for orienting toward stimuli that are good candidates for being mom, and another for taking whatever it can get, for storing a memory of anything that the chick might be exposed to. The first system will choose an adult chick (or even a stuffed duck) over a box as its go-to-caregiver, but if there’s nothing else around, the second system will lead the chick to settle for the box.
— Marcus (2004, 104)
The first system here would correspond to the top half of the meaning cycle, the second system to the bottom half. Likewise, a reader looking for guidance in a turning sign or “scripture” will ‘seek until he finds’ and then use whatever he finds to guide his practice (including any further seeking); the niche in meaning space that yearns for fulfillment will be filled regardless of which text the seeker ‘finds.’