Learn Hardcore Russian: Он сам делает домашнее задание.

Он делает домашнее задание. – He is doing his homework. (Neutral statement.)
Он сам делает домашнее задание. – He is doing his homework himself.
This can imply:
- He is not getting help from anyone, or
- He, and not someone else, is the one doing it.

So сам adds emphasis: either without help or as opposed to someone else (context decides which nuance is stronger).

Is сам the same as saying by himself or alone in English?

Not exactly; Russian makes a distinction:

Он сам делает домашнее задание.
Focus on: he does it himself (not his parents, not a tutor).
It’s about who performs the action.
Он делает домашнее задание один.
Focus on: he is alone while doing it (no one is with him).
It’s about being physically alone.

In many contexts, English uses by himself for both ideas, but Russian often chooses between сам (no help / he is the doer) and один (physically alone).

Is сам some kind of reflexive pronoun like себя?

No. In Russian:

Сам is an intensifier meaning oneself / himself / herself in the sense of emphasis:
- Я сам сделаю. – I’ll do it myself.
- Она сама приготовила ужин. – She herself cooked dinner.
Себя is a reflexive pronoun (like myself / yourself / himself in a grammatical sense):
- Он видит себя в зеркале. – He sees himself in the mirror.
- Она заботится о себе. – She takes care of herself.

In Он сам делает домашнее задание, сам is emphasizing он, not reflecting the action back to him in a grammatical way.

Where should сам go in the sentence? Can I move it?

The most neutral and common place is right after the pronoun:

Он сам делает домашнее задание.

Other positions are possible, with different emphases:

Сам он делает домашнее задание. – Stronger emphasis on он (he, specifically).
Он делает домашнее задание сам. – Slightly more emphasis on without help; it can sound like answering the question “How does he do it?” – He does it himself.

All three can be correct in the right context, but Он сам делает домашнее задание is the standard textbook version.

What tense and aspect is делает?

Делает is:

Tense: Present
Aspect: Imperfective
Verb: делать (to do, to make)

So Он сам делает домашнее задание means he is currently doing it or generally / habitually does it himself (depending on context).

If you wanted to talk about a completed action, you would typically use the perfective pair сделать:

Он сам сделал домашнее задание. – He did his homework himself (it’s finished).

Why is it домашнее задание and not домашний or домашняя?

The adjective домашнее agrees with the noun задание in:

Gender: neuter
Number: singular
Case: accusative

Задание is a neuter noun (оно), so the dictionary form is:

домашнее задание – homework (literally: home assignment)

If the noun were masculine or feminine, the adjective would change:

домашний суп – home(-made) soup (masculine)
домашняя работа – homework / housework (feminine)

Why is домашнее задание in the accusative case? It looks the same as nominative.

Домашнее задание is the direct object of the verb делает, so it must be in the accusative case.

For neuter inanimate nouns, the accusative form is identical to the nominative:

Nominative: домашнее задание – homework (as a subject)
Accusative: домашнее задание – homework (as an object)

So even though you don’t see a change in form, you know it’s accusative from its role in the sentence: What does he do? – Homework.

Why is there no word for his before домашнее задание?

Russian often omits possessive pronouns (like его, её, их) when the owner is clear from context, especially with family members, body parts, and personal belongings.

In this sentence:

Он сам делает домашнее задание.

It is obvious that a person is usually doing his own homework, so saying его домашнее задание is often unnecessary and can sound heavier or more contrastive.

You can say:

Он сам делает своё домашнее задание.

This strongly emphasizes his own homework (for example, not his brother’s). But in many everyday contexts, Russian just omits the possessive.

Why is задание singular when English ‘homework’ is uncountable?

Russian sees it differently:

Домашнее задание literally means a home assignment (one task or set of tasks).
It is a countable noun:
- одно задание, два задания, много заданий – one assignment, two assignments, many assignments.

English homework is usually uncountable, but Russian задание is countable, so the default phrase is singular домашнее задание.

You can also use the plural:

Он сам делает все домашние задания. – He does all the homework assignments himself.

Can I drop он and just say Сам делает домашнее задание?

Yes, in the right context.

Russian often drops subject pronouns when the subject is clear from previous sentences or from the situation. For example, if you’re already talking about this boy:

Раньше ему помогали родители, а теперь сам делает домашнее задание.
Before, his parents helped him, but now he does his homework himself.

Here сам делает… is understood as он сам делает….

However, in isolation (with no context), the full Он сам делает домашнее задание is clearer and more natural for a learner to use.