Haecceity (from the Latin haecceitas) is usually translated as “thisness.” Duns Scotus is believed to be the first person to use the word to denote the wholly unique components that make a person or object unlike any other person or object. In a certain sense it is the emergent quality of a thing that we recognize as being one of a kind and therefore worth great value.
A sensitivity to “thisness” is one of the central muscles of a poetic mind. With it we move out of categorizing all stones as “stones,” which is a time saving device, into contemplation of this particular stone, which is a time occupying device. We pick up the stone, we turn it over, we appreciate it for it’s thisness. This of course is not a muscle exclusive to the poetic mind. The scientific mind also requires this working, this using of effort. In thisness the scientist and the poet stand together — in curiosity, in wonder sometimes, at the profoundness of this one unique thing, this anomalous data-point varying from all other data-points, yet clustering into that cloud of similarity that evokes the classification.
We make sense of the world by placing each thing into these clouds, these clouds of similar qualities, or similar appearances, or rigorous distinctions. Species, elements, personalities, types, kinds — the categories at least less numerous than the objects inside them.
The scientist must contemplate an objects thisness to determine which clouds the object belongs in, creating complicated Ven diagrams to nudge the object into understanding. Understanding arising out of the process of classification.
Thisness for the poet, however, is more about gratefulness, appreciation, and delight in somethings particular charm. While all rainbow trout are beautiful, this one is a little deeper in the belly, has a little larger tail, and those combinations make THIS trout more beautiful or significant or trouty than the others.
Finding the unique in all things is not possible for us, but perhaps is the pleasant task of God.