Questions & Answers about Семинар начинается в десять часов.
Why is there -ся at the end of начинается?
The suffix -ся makes начинаться an intransitive verb meaning “to start” (to begin on its own). Without -ся, начинать is transitive and means “to start something.” Russian uses -ся on many verbs to indicate that the action happens to or by the subject itself.
Why is there в before десять часов?
The preposition в + accusative case marks a specific point in time, equivalent to English “at.” When giving clock times in Russian you always use в + time (e.g., в три, в пять часов, в десять).
Why is десять unchanged and часов in the genitive plural?
Numerals from 5 and up require the noun to be in the genitive plural. So after пять, шесть, … up to десять (and beyond), you say часов (not час or часа).
Can I drop часов and say just в десять?
Yes. In everyday speech you can omit часов when it’s clear you’re talking about hours: Семинар начинается в десять. It’s concise and perfectly natural.