Learn Hardcore Russian: Мой друг знает секрет.

In Russian possessive pronouns agree in gender, number, and case with the noun they modify. Друг is a masculine noun in the nominative singular, so you use Мой (masculine nominative), not Моя (feminine) or Моё (neuter).

What gender and case is друг, and how do you know?

Друг (“friend”) is masculine and here it’s the subject of the sentence, so it’s in the nominative case. Nouns in the nominative case usually answer the question “who?” or “what?”—in this case, “Who knows the secret? My friend.”

What case is секрет in and why does its ending not change?

Секрет is the direct object, so it takes the accusative case. Because секрет is an inanimate masculine noun, its accusative form is identical to the nominative. That’s why you still see секрет rather than a different ending.

What does the ending -ет in знает indicate?

The verb знать (to know) in the present tense is conjugated as: я знаю, ты знаешь, он/она/оно знает, мы знаем, вы знаете, они знают. The ending -ет marks the 3rd person singular (“he/she/it knows”).

Where is the stress in знает and секрет, and how do you pronounce them?

In знает, the stress is on the first syllable: ЗНА-ет. In секрет, the stress is on the second syllable: се-КРЕТ. Correct stress is important for being understood.

Why is the neutral word order Мой друг знает секрет rather than rearranging the words?

Russian has fairly flexible word order, but the default “neutral” order is Subject–Verb–Object (SVO), just like in English. Changing it (e.g. Секрет знает мой друг) puts extra emphasis or a stylistic twist on whichever word you move to the front.

Could I use тайна instead of секрет, and would anything change grammatically?

Yes, тайна also means “secret,” but it’s a feminine noun. You would say Мой друг знает тайну. Notice тайну is in the accusative feminine singular (ending –у), so the form changes accordingly. Semantically, тайна can also carry a more “mysterious” or poetic nuance.