dithering is a strange technique that grew out of more general principles:
isolation versus pattern and mass - a mark that is unique or distanced from similar marks is read as an individual element and does not, therefor, typically contribute to sub-elemental workings such as shading a greater surface. the more regular something is, the less important it becomes, allowing it to become part of something else. Dithering and other textures rely on this subversion of the element to achieve its goals.
scale, contrast, and relation to the whole - small marks are easier to subvert than large marks, and marks that contrast less with the dominant color are also.
nonindependence of shape - pixels can very readily create shapes larger than themselves by touching the pixels around them, obviously to the cardinal points but also across diagonals. This second creates the checkerboard lattices that we read as "both white and black" or "gray" in a simple dither. However, it is important to recognize that shape is independent of size and that it is merely illustrating larger ideas of continuity very effectively:
ANY FORM WHICH TOUCHES ANOTHER IS CONNECTED VISUALLY REGARDLESS OF AREA OR SHAPE.
The connection can range from sharing a point to sharing an entire entity (and which point the shapes become one). the reason this is important is because it means that any cluster of shapes which touch each other activate this same blending space whether they are sqaures in a grid or bubbles of soap or people holding hands.
On a final note since i'm late for leaving, also recognize that positive and negative space have no meaning for continuity of shape. a bunch of nearly-touching black circles is also a bunch of barely-touching white diamonds and vice versa :
