Let me not to the marriage of true minds
Admit impediments. Love is not love
Which alters when it alteration finds,
Or bends with the remover to remove.
O no! it is an ever-fixed mark
That looks on tempests and is never shaken;
It is the star to every wand'ring bark,
Whose worth's unknown, although his height be taken.
Love's not Time's fool, though rosy lips and cheeks
Within his bending sickle's compass come;
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom.
If this be error and upon me prov'd,
I never writ, nor no man ever lov'd.
The speaker ponders the beauty of love by saying that he never accepted the fact, that true love or “the marriage of true minds” admits the obstacles or diriment. True love will not change even when things get modified by tough situation or with the departure of the lover. If it deviate its course, then love isn’t true love. True love is an ever fixed mark like a lighthouse which can never be shaken by any storm. It guides every lost ship like a guiding star ‘Polaris’ (also known as “the North Star”) whose value cannot be measured and still used by sailors to navigate. Love can never be fooled by time, even-though physical beauty (pink lips and cheeks) falls within the range of time’s sickle (curved) blade. Love will never alter with hours and weeks, but rather it endures until death (last day of life). He says that if his statement is wrong or his own behaviour serves as evidence for his thoughts on love then he will forswear all he has written and no man has ever loved in this world.
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Source: The Norton Anthology of English Literature: Volume One Seventh Edition (2000)