One theme that can be seen is the irrationality of love. We especially see this theme when Helena points out in the opening scene that she is just as beautiful as Hermia, yet, Demetrius has abandoned her for Hermia instead. Helena points out that Demetrius's choice is neither rational nor based on any objective reason, such as beauty, but instead irrational because love is governed by imagination, as we see in her lines:
Love looks not with the eyes, but with teh mind;
And therefore is wing'd Cupid painted blind.
Nor hath Love's mind any judgement taste. (I.i.239-241)
Another theme found in the play is the irrationality of human beings in general. We especially see this theme portrayed in the animosity the four lovers display once Puck muddles them, making the two men pursue Helena instead of Hermia. Puck rightly sees Helena's response of believing the two men are mocking her as irrational, but he further sees her response of believing her best friend to be in on the joke as equally irrational. We especially see the theme of the irrationality of human beings portrayed in Puck's famous line, "Lord, what fools these mortals be!" (III.ii.116).
A third theme we see presented in the play is reality vs. illusion. Shakespeare makes it very clear that he views reality as being dominated and manipulated by illusion. We see one instance of this theme presented in Puck's manipulation of the Athenians in the forest. Puck creates a completely different reality for all of the Athenians by first using enchantment to manipulate Lysander and Demetrius into falling in love with Helena and then using enchantment to correct the situation. He further creates a different reality for the mechanicals, especially Bottom, by turning Bottom into a donkey.
We further see the theme of reality vs. illusion in the mechanicals' aspiration to write and perform a play. The mechanicals, who are Athenian laborers, are being particularly ambitious in desiring to present this play, especially because they are uneducated and have never written nor ever performed a play before. Philostrate, the man in charge of organizing Theseus's wedding celebration, describes their ambition and the reality of their abilities best when he describes them as "[h]ard-handed men that work in Athens here / Which never labour'd in their minds till now" (V.i.76-77). However, despite the mechanicals' visions of putting on a grand performance, especially Bottom's vision, the reality is that they turn a tragedy into a play that is extremely laughable, as we see from both our own observation of their performance and also from the other characters' responses to the performers.