Excerpted from poetryfoundation.org:
And so, in its dark-glass way, “If—” reflects modern uncertainty after all. It’s a masterpiece of timing, of structure, of rhetoric (the genre that Yeats pointedly contrasted with poetry). But the more you read it, the more you hear a countersong beneath the assurance. In that long series of perfectly balanced clauses, you hear a mounting fear that the child won’t succeed. The sentence keeps building; the number of required conditions keeps growing. Maturity starts to seem like a very big “if.”
What is dark-glass way?