Clitics: jsem se, bych si

Short unstressed words (clitics) such as se, si, jsem, bych stand in second position in Czech, right after the first word or phrase of the clause.

• When several of them meet, the auxiliary comes first, then se/si: jsem se, jsme si, bych se, byste si.
• In the past tense the auxiliary shows the person: jsem, jsi, jsme, jste. The third person has no auxiliary: Petr se vrátil. Děti se smály.
• In the second person singular, jsi se usually becomes ses and jsi si becomes sis: Kdy ses vrátil?
• In the conditional, use bych, bys, by, bychom, byste; by serves both he/she and they: Rád bych se podíval.
• A name in the vocative (Petře, ...) does not count as the first position.