Final answer:
Eliot gained the idea from the French Symbolists that symbolism in art can be used to express ideas, feelings, or visions instead of focusing on realistic representations of the natural world.
Step-by-step explanation:
The idea that Eliot gained from the French Symbolists is that symbolism in art can be used to express ideas, feelings, or visions instead of focusing on realistic representations of the natural world. The Symbolists believed that the use of color, lines, and other artistic elements could evoke emotional experiences in the viewer. This concept of symbolism was influential in Eliot's poetry, particularly in his famous work 'The Waste Land', where he used symbolic imagery to express the disillusionment and despair of the post-World War I era.