Shall I bend low, and in a bondman's key,

With bated breath and whispering humbleness.

William Shakespeare (1564-1616): The Merchant of Venice. Act i. Sc. 3.

Scorn not the sonnet. Critic, you have frowned,

Mindless of its just honours; with this key

Shakespeare unlocked his heart.

William Wordsworth (1770-1850): Scorn not the Sonnet.

That golden key

That opes the palace of eternity.

John Milton (1608-1674): Comus. Line 13.