Øystein Sveum Moen poses an interesting question about shade and shadow:
I constantly end up in discussions whether something’s in the shade or shadow. Is there a clear definition of the difference between these two? Where I come from (Norway) we have a single word covering all forms of light blocking darkness.
Both shade and shadow come from the same Old English word sceadu, “shade, shadow, darkness.” The general definitions given for both words are almost identical in the OED:
shadow: I. Comparative darkness. 1. a. Comparative darkness, esp. that caused by interception of light; a tract of partial darkness produced by a body intercepting the direct rays of the sun or other luminary.
shade: I. Comparative darkness. 1 a. Partial or comparative darkness; absence of complete illumination; esp. the comparative darkness caused by a more or less opaque object intercepting the direct rays of the sun or other luminary.
Both words have numerous uses. For example, shade can mean “the ghost or spirit of someone dead.” Capitalized, Shadow is a term given by Carl Jung to the aspect of the human personality formed by fears and unpleasant emotions. The OED entries for shade and shadow include about 40 different definitions for each of the words.
Used in the sense of “comparative darkness,” the words are sometimes, but not always interchangeable.
Shade is what one seeks on a hot sunny day. We sit or walk in the shade. Plants that do well in the shade are called shade-loving plants.
Shadow usually refers to a shape cast by an object that blocks the sun. A person casts a shadow in the shape of the human body. Figuratively, however, one might say that a younger brother lives “under the shadow” or “in the shade” of an older brother.
Both words have emotional connotations. To those of us who live in hot climates, shade has pleasant and soothing associations. Shadow is evocative of something mysterious or threatening, especially in the plural. Stalkers lurk in the shadows. As the sun sets, evening shadows fall, concealing what was formerly visible and making the ordinary strange.
Addressing the difference between shade and shadow in Modern English Usage, H.W. Fowler concludes that “shadow is to shade as pool is to water.” He points out that “shady means full of shade, but shadowy like a shadow.” Shade, therefore, denotes a general state, while shadow implies a shape.