"Evil is like a shadow - it has no real substance of its own, it is simply a lack of light." ( part of one of these days' thought)

Was wondering about this since I saw it. Does one sit in the shadow or does one sit in the shade? Do cows lie in de shadow of the trees or do they lie in the shade of the trees? How are these words used properly?

Evil is like a shadow but what would we do without shadow? (shade?)

The shadow is generally in relation to the thing casting the shadow. The shade is the thing irrespective of what is casting it. You might speak of the shadow of a tree but you'd be more likely to speak of the shade if something is using it to avoid the direct sun.

Shade tends to have a more positive aspect than shadow. Relief from heat rather than lack of light.

There is a difference, but it gets kind of wordy. A thing (tree, building, person) casts a shadow but gives shade. We sit (and cows lie) in the shade of a tree. The tall building made the entire street shady. But a potential attacker lurks in the shadows.

Being "in another person's shadow" could literally mean you're standing in the dark shape they cast on the ground, but most of the time it's taken to mean that, no matter how wonderful your deeds have been, the other person's deeds have been greater, received more recognition, etc.

Then there is the not-much-used-but-still-commonly-understood use of the word shade to mean a ghost. The Widow Wonka thought she saw her husband's shade looking in the window.

Was that clear enough, or not yet?

Shade also implies light all around, whereas shadows can lurk in dark rooms and alleys as well as under trees on sunny days.

It was meant to be wordy. All your comments have cleared it up. I now understand the thought of that day better.
We only have the one word 'shadow'. It's nice English has this distinction.

All your comments have cleared it up. Well, that's one!