The phrase "Words are the fossils of thought"

 The phrase "Words are the fossils of thought" suggests that words are the preserved remnants or impressions of once-living, dynamic thoughts. Thoughts are fluid, fleeting, and complex, while words are concrete, fixed, and often simplify or "fossilize" those thoughts.

Here are some alternate phrases or ways to express a similar idea, with slightly different nuances:

Focusing on words as limited representations:

• Words are the echoes of thought. (Suggests a fainter, less direct representation)

• Words are the shadows of thought. (Emphasizes that words are a mere outline, not the full substance)

• Words are the containers of thought, but often too small. (Highlights the limiting nature of language)

• Language traps the fluid nature of thought. (More active, showing language's effect on thought)

• Thoughts outrun the words we use to catch them. (Emphasizes the speed and complexity of thought)

• Words are but snapshots of a flowing stream of consciousness. (Compares thought to something continuous and words to discrete moments)

• What we say is a pale reflection of what we truly mean. (Focuses on the inadequacy of expression)

Focusing on words as remnants or evidence:

• Words are the footprints of our minds. (Suggests traces left behind)

• Words are the crystallized forms of ideas. (Implies a process of solidification)

• Words are the fixed points of fleeting ideas. (Highlights their stability in contrast to thought's transience)

• Our spoken words are the enduring traces of our inner world. (Broader, encompassing more than just "thoughts")

More metaphorical or poetic:

• Every utterance is a tombstone for a living idea. (More dramatic, emphasizing the "death" of the original thought)

• Thought, once spoken, becomes a caged bird. (Suggests restriction and loss of freedom)

The best alternative depends on the specific nuance you want to convey.