What are the main themes of the Shakespeare's Sonnet 138?

There are two main themes in Shakespeare's Sonnet 138. The
two main themes developed in the sonnet are lies and
truths.

The theme of lies is developed through the double
meaning used in the word "lies" within the text:

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When my mistress swears that she is faithful/ I
do believe her though I know she
lies

Here, the speaker uses
the word "lies" is a polysemy (has a double meaning). The word lies refers to the fact
that she is not telling the truth and that she physically lies with other
people.

Therefore, this idea of lying is thematically
created through the repetitive use of the words which coincide with the term lie:
deceit, foolishly, untruths, ugly truth, and disguise.

To
mirror this theme, the theme of truths exists within the poem as well; although, this
theme is more implicit. The speaker admits that he knows his mistress is lying, but his
acceptance of her lying creates a truth for him. This theme is defined through the use
of the following words: believe and pretense of truth.

It
is through each's acceptance of lies and omittances of truths which both the speaker and
the mistress find truth in their realtionship.