Tartuffe, or The Impostor, or The Hypocrite, was written by Molière in 1664, at a time when the Académie française was actively involved in regulating French language, grammar, and literature, including French drama.

The standards that the Académie imposed on French drama were derived from the writings of the French neoclassicists, who based their principles of drama on the plays of Aeschylus, Sophocles, Euripides, and other ancient Greek playwrights from the 5th century BCE, and on Aristotle's Poetics, written around 355 BCE.

The French neoclassicists interpreted Poetics as Aristotle's rules for Greek drama, rather than simply Aristotle's observations and analysis of plays that were written a hundred years before Aristotle wrote Poetics.

The Académie decreed that French plays must conform to the "three unities" of action (a single, unified plot, and no subplots), of time (the action of the play must occur within a single day), and of place (that the play occurs in a single location).

French plays of the period were also required to conform to standards of language and composition. Plays must be composed exclusively of alexandrine couplets, which are rhymed couplets (two lines) written in iambic hexameter—twelve syllables per line, in an iambic rhythm pattern (da-DUM).

da-DUM da-DUM da-DUM da-DUM da-DUM da-DUM

Additionally, each line must contain a caesura, or a pause, between the 6th and 7th syllable of each line.

da-DUM da-DUM da-DUM [pause]da-DUM da-DUM da-DUM

The couplet could be split between two characters, but each line still had to conform to the "rules" of dramatic construction.

One further requirement is that the two lines of the couplet must form a complete thought.

These are the first two lines of Tartuffe, in the original French:

MADAME PERNELLE:
Allons, Flipote, allons; que d'eux je me délivre.
Al-LONS, Fli-POTE, al-LONS; [caesura] que D'EUX je ME dé-LIVRE.
ELMIRE:
Vous marchez d'un tel pas, qu'on a peine à vous suivre.
Vous MAR-chez D'UN tel PAS, [caesura] qu'on A peine À vous SUIVRE.

There have been no successful translations of Tartuffe into English verse that maintain the iambic hexameter of the original play. Most translations of Tartuffe into English verse are done in iambic pentameter (ten syllables per line), such as the translation of these same two lines by Richard Wilbur:

MADAME PERNELLE
Come, come, Flipote; it’s time I left this place.
Come COME Fli-POTE; [caesura] it's TIME I LEFT this PLACE.
ELMIRE
I can’t keep up, you walk at such a pace.
I CAN'T keep UP, [caesura] you WALK at SUCH a PACE.

Structured writing such as rhyming couplets or writing in specific meter is largely lost in most Western playwriting today. During Moliere’s era, it was much more usual to write with a specific meter in mind, and different meters were generally used for different genres.

Rhyme schemes, especially rhyming couplets, are often used in comedy. There are several reasons for this. Foremost, rhyming couplets have a quick, zippy quality to them that keeps the action of the play moving along at a good pace. The writing style ensures the actors get the dialogue out quickly and on rhythm.

Secondly, rhyme schemes offer a wealth of ways to create comedy. An unexpected word might be used to rhyme with another, characters might finish each others’s couplets, and certain phrases might be reused throughout the play. There is also usually not as much psychological depth expected from shows with rhymes written into the language, which suits comedy well.

Third, and this is more of a by-product, but rhyming couplets are often incredibly easy to memorize, making the script easier to tackle for actors and actresses.

Lastly, Moliere was a showman, and likely wanted to show off. The rhymed couplets in Tartuffe are surely one aspect that has kept the show popular into modern times.

Moliere's Tartuffe is written in a verse form known as the "alexandrine". This consists of twelve syllable lines with a medial caesura. The form was named in reference to medieval "Alexander" romances and became the standard line of classical French poetry, much like the dactylic hexameter in Greek or the iambic pentameter in English. The great French writers of tragedy such as Pierre Corneille and Jean Racine wrote in alexandrine couplets.

Tartuffe is a comedy rather than tragedy but achieves many of its comic effects by inverting tragic conventions and expectations. Thus much of the success of Tartuffe depends on taking tragic conventions and mocking or distorting them. This produces humor through creating a tension between the heroic form and diction of many speeches and distinctly non-heroic content. The hypocrisy of Tartuffe himself is emphasized in the contrast between his elaborate surface piety and ornate religious language and his actual reality as a hypocrite and swindler.

According to notes by the Theatre of Western Springs, Tartuffe has an added challenge it its delivery with the use of the rhyming couplet because:

The frenetic nature of the play’s action demands that the text be spoken quickly. The amount of vocal dexterity and lung power it takes to speak the lines challenges the actors’ lungs, lips and jaws. And even though some actors find the rhyming couplets easier to remember, those couplets can be unforgiving should memory fail.

Consequently, since the play goes fast and the commedie francaise was famous at the time for its speedy, witty and elaborate complications, an actor was more likely to remember his lines when they rhymed. Another thing is that if the actor for any reason forgets his lines, he could always substitute one word for another.

In other words, it was a device to make the play flow easier, and allow ease for the challenging roles to be played.