The verbs yemek and demek change the e in their stem to an i when followed by a y:

English	First form	Second form	Third form
Eat.	Ye.	Yiyin.	Yiyiniz.
Say hello.	Merhaba de.	Merhaba diyin.	Merhaba diyiniz.

As a reminder, here are the functions of the three forms of the imperative again:

The first form is used for addressing a single person informally
The second form is used for addressing a single person politely or multiple people informally
The third form is used for addressing a single person in a very formal way or multiple people politely

While yemek can be both transitive and intransitive, demek is always transitive. What do those mean, you ask?

Transitivity is a linguistic term that is related to a verb's relation with objects. Some verbs take one object (e.g "I love you."), some take two (e.g "I gave John₁ a book₂.", and some take none (e.g "I ran."). Verbs that do take an object (or two objects) are called transitive. Verbs that do not take objects are called intransitive.

In the sentence "I gave John a book", "John" is the indirect object and "a book" is the direct object. You will learn more about these terms in later lessons.

Breakdown of Merhaba de.