The verb съм (to be)

Съм (to be) is the most common Bulgarian verb. Its present forms are: аз съм, ти си, той/тя/то е, ние сме, вие сте, те са. The polite Вие always takes сте.

These forms are short, unstressed words (clitics), so they follow three rules:

• They never start a sentence: Гладен съм. (I am hungry.), never *Съм гладен.
• In a question they come right after ли: Ти гладен ли си? (Are you hungry?)
• In a negative sentence they come right after не: Аз не съм уморена. (I am not tired.)

For the time, the day or the weather, use е with no subject: Днес е неделя. (Today is Sunday.), Студено е. (It is cold.)