Not all Class 2 verbs undergo this change. These forms are often called the active past participle I. The masculine singular evolved from an earlier *-лъ that vocalized (cf. Polish "-ł"). In Ukrainian, there are 2 different future tenses for imperfective verbs. The first form, called "simple" ("проста форма"), formed by adding to the infinitive of the verb the following endings, which are derived from the Common Slavic verb "*jęti" (Present stem: jĭm−):  The second form, called "compound" ("складена форма"), is to take the present tense conjugation of the verb "бути" and use it with the infinitive of the verb. Thus,  This will translate as "will eat" with the appropriate personal pronoun. The two forms do not differ in function or semantics. However, the "compound" form tends to be used more often, and is the only way to form a future of the verb "бути". The imperative mood is used to give commands. It exists in only the present tense in Ukrainian. There are no forms for the 1st person singular. In Ukrainian, the imperative mood is formed from the present stem of the verb plus the following endings (The example is based on Ukrainian "пити"):  The first set of endings is to be used for stems that end in a dentals ("з, д, т, с, н," and "л"). The second set of ending is used for stems that end in a vowel. The third set of endings is used for stems that end in labials or post-alveolar sibilants ("б, в, м, п, ф, ш, щ, ч, ж," and "р"). The fourth set of endings is used with verbs whose unaffixed form (no prefixes or suffixes) have the stress on the ending in the first person singular of the present tense. As well, most Class 2 verbs and those verb roots ending in a consonant plus "л" or "р" take these endings. Thus for example, "бери" and "вибери". Class 5 verbs take the first set of endings, but undergo an archaic form of iotation, so that "дь" becomes "ж" (rather than "дж"), for example, "їжте" < "їд+ьте".