If we are thinking about the terminator dividing the object into the side of light and the side of shadow, the form shadow refers to this general grouping on the shadow side. Core shadow, reflected light, and ambient occlusion are more specific terms referring to parts that make up that shadow region. As for your answer sheet, it looks pretty spot on! The only thing I would note is that the dark halftones are more contained to a smaller portion as they transition into the lighter halftones. A smaller detail, but it's good to be aware of it, especially as this change can happen pretty quickly under strong/direct lighting.

I went back a few days later to repeat and did the extra. For some reason, this was easier in some ways but harder in others. With the glossy surface and increased ambient light, I'm not sure I completely got it. If anyone solved this, too, please reach out!

Nice! Just a few things to keep in mind: - The core shadow will typically be more along the same lines as the terminator. - The dark halftones will be a smaller area, the area of shadow before other factors (ie reflected light) take effect. - Reflected light affects any area near another surface receiving light, so this will also affect the left cheek, jaw, and eye/note bumps to varying degrees (depending on the strength of light coming from the nearby surface). - The highlight in this scenario will be more limited, still in the same areas you correctly marked, just smaller. The surface texture of the monkey appears matte, so that will limit the amount of reflectivity to create a highlight. - Ambient occlusion will also affect any crevice with a pocket of shadow, not just between the object and ground. You can find some areas around the eye surface crevices, and the nose/ear/mouth bumps. These may be smaller corrections, but understanding the components of light both separately and how they work together early on can really help in the long run once you enter more complex subjects, as even the most masterful and complicated scenes build on top of these principles. Happy drawing and I hope this helps!

My attempt of drawing the modelling factors with the example white ball. I found it quite hard to make the ball appear white while also differentiating the shadow mid-tones and the darkest cast shadow. Critique welcome!