Learn Hardcore Russian: Я добавляю немного масла в суп.

Because words like немного, мало, много, сколько take a noun in the partitive genitive to express “some of” or “a little of.” Even though масло is normally nominative or accusative when it’s the subject or direct object, after немного it switches to genitive (масла) to show you’re adding “a bit of oil,” not the whole oil.

Why is суп in the accusative case after в (в суп)?

The preposition в can govern either the prepositional case (location: “in/at”) or the accusative case (direction/motion: “into”). Here you are putting oil into the soup, so you use в + accusative (в суп). If you wanted to say “the spoon is in the soup,” you’d use в супе (prepositional).

Why do we say немного масла instead of несколько масла?

Несколько is used only with countable nouns (e.g., несколько яблок, несколько книг). Масло is an uncountable (mass) noun—“oil” you can’t count in pieces—so you use немного (or мало/много) + genitive to talk about an indefinite quantity: немного масла.

What is the aspect and grammatical person/number of добавляю? What would be its perfective form?

Добавляю is the imperfective aspect, 1st person singular, present tense. It describes an ongoing or habitual action (“I am adding” or “I add”). The perfective counterpart is добавить; in the future you’d say я добавлю немного масла в суп (“I will add a bit of oil to the soup” as a single completed action).

Can you omit я and just say Добавляю немного масла в суп?

Yes. Russian verbs are conjugated for person and number, so the subject pronoun is often dropped when it’s clear from context. Добавляю… by itself already means “I add…” or “I am adding…”

Where do you place the stress in добавляю?

The stress falls on the syllable вля́: до-ба-вля́-ю. Misplacing it (e.g. “до́бавляю” or “доба́вляю”) would sound unnatural.

Could you swap добавляю for кладу or подсыпаю here?

Potentially, but with slight differences:
• Кладу немного масла в суп – literally “I lay/put a bit of oil in the soup.” Grammatically fine, but класть is more generic (“to put”), whereas добавлять specifically means “to add (an ingredient).”
• Подсыпаю немного масла в суп – “I sprinkle/pour a bit of oil into the soup.” It’s more colloquial and implies sprinkling small amounts, but добавляю remains the standard choice when talking about adding ingredients.

Why is масло singular? Could it ever be in plural?

Масло is a mass (uncountable) noun in Russian, so it normally appears only in the singular when referring to the substance “oil.” You might see a plural масла if you talk about different types of oil (растительные масла, животные масла) or bottles of oil, but not when you mean “some oil.”