Finally (at least probably finally, unless I ever return to the topic later), these three images exemplify shadows as puzzling abstractions.  

The human eye tries to decipher visual abstractions.  Maybe this is a brain-related puzzle-solving pleasure function, or maybe we are hard-wired by pre-history to mentally understand what we see, so we can distinguish between what might eat us and what we might eat.  

At any rate, the patterns of the first two might initially imply foliage (benign, no threat, but probably no food, either, unless bananas or mangoes are near).  But the backgrounds are puzzling, obviously not grass or ground.  As you may have noticed, many of the tree-shadow photos in earlier shadow posts were taken on grass lawns or snow.  Bright, sunny, high-contrast days provoke this modern human response: Get the camera and take a picture.

The backgrounds in the first two are water, specifically the Pacific Ocean.  Both show shadows thrown by clouds over the passage between Maui and Molokai in early stages of sunset.  

This last intrigues me because it seems very organic, as in mammalian.  It thus might raise possible threat or food questions.  Is this part of a nearby moose, about to move? And even though I took it, whenever I run across this image in my Lightroom catalogue, it momentarily triggers a question whether this is really somehow the lower backend of a moose, standing in snow.  And each time it requires confirmation (from memory, less than from the images) that these are shadows extending from birch trees in our yard.  And thus benign, if visually puzzling or possibly menacing in a fictional Film Noir sense.

I am not going to try to articulate a Grand Unified Shadow Theory.  Shadows interest me for different reasons.  And one of the contradictions of photography, - which, after all, tends to bring detail to light for examination, study, and perhaps appreciation -  is that shadows by nature diminish or completely hide detail.  They thus provide large, dark fields that resist micro understanding, apart from any edges that are in transit from light to dark.  Perhaps those transitions - those penumbras - need future posts. Maybe someday.