Learn Hardcore Russian: Я кладу проездной в кошелёк, чтобы не забыть его дома. - I put my travel pass in my wallet so as not to forget it at home.

кладу – 1st person singular of класть (imperfective)
- Focuses on the process or the current action: I am putting / I put (as a general habit).
- In this sentence it sounds like you are describing what you are (now) doing or typically do.
положу – 1st person singular of положить (perfective)
- Focuses on the result, usually future: I will put.
- Я положу проездной в кошелёк, чтобы не забыть его дома = I will put the pass in my wallet so I don’t forget it at home.

So the given sentence with кладу can be understood as either:

a description of what you’re doing right now, or
a habitual/regular action (“I (always) put my pass in my wallet so I don’t forget it”).

Using положу would sound more like a concrete future decision or plan.

What exactly is проездной here – an adjective or a noun?

Historically проездной is an adjective meaning travel / transport / fare-related (from проезд – passage, ride).
In everyday speech, it’s used as a shortened noun for проездной билет = travel card / transit pass.

Full phrase: проездной билет (literally “travel ticket”)
Spoken everyday version: проездной

Grammatically in this sentence, проездной functions as a masculine inanimate noun in the accusative singular, which for such nouns looks the same as the nominative:

Nominative: проездной
Accusative: проездной (same form)

Why is проездной in the accusative case?

The accusative case is used for the direct object of a transitive verb – the thing directly affected by the action.

Verb: кладу – I put
What do I put? проездной – that is the direct object.

So проездной must be in the accusative.

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

Nominative: проездной
Accusative: проездной

Why is it в кошелёк and not в кошельке?

Russian uses different cases after в depending on movement vs location:

в + accusative = into somewhere (direction, movement)
в + prepositional = in/inside somewhere (static location)

In this sentence:

в кошелёк – accusative → into the wallet (movement, you are putting something into it)
в кошельке – prepositional → in the wallet (already inside, location only)

So Я кладу проездной в кошелёк = I’m putting my pass into the wallet.

What’s the difference between кошелёк and бумажник?

Both can translate as wallet, but there are nuances:

кошелёк
- Very common, general word for wallet or coin purse.
- Can be used for both men’s and women’s wallets, including small purses.
бумажник
- More specifically a billfold / wallet for paper money, often a man’s wallet.
- Sounds a bit more “solid” or traditional.

In this sentence, кошелёк is the most natural and widely used word.

Why is it чтобы не забыть его дома and not чтобы я не забыл его дома?

Both structures are grammatically possible, but they are used in different ways:

чтобы + infinitive (when subject is the same in both clauses)
- Я кладу проездной в кошелёк, чтобы не забыть его дома.
- Literally: I put the pass into my wallet, in order not to forget it at home.
- Very common and natural when the doer is the same: “I put … so as not to forget.”
чтобы + finite verb (subjunctive-like: чтобы я не забыл)
- …чтобы я не забыл его дома.
- Sounds more like a wish/hope or desired outcome: “…so that I won’t forget it at home.”
- Grammatically fine, but a bit heavier and more “spoken-emphatic” here.

In everyday speech, with the same subject in both parts, Russian strongly prefers чтобы + infinitive.

What does его refer to – the wallet or the pass?

Его is a masculine singular pronoun and here it refers to проездной:

проездной – masculine noun
кошелёк – also masculine

So how do we know which one is meant?

Logic: you are more likely to forget your pass at home than your wallet, given the context.
Proximity & structure:
- You just mentioned the object you are taking care of: проездной.
- The idea is “I put my pass in the wallet so I don’t forget it at home.”

Technically, pronoun reference is ambiguous if you look only at grammar, but in real language this sentence is interpreted as referring to проездной.

Could we omit его and just say …чтобы не забыть дома?

Yes, you can say:

Я кладу проездной в кошелёк, чтобы не забыть дома.

This is still understandable and fairly natural. Russian often omits pronouns when the referent is clear from context.

Nuance:

With его:
- чтобы не забыть его дома – specifically “so I don’t forget it at home” (explicit reference to проездной).
Without его:
- чтобы не забыть дома – “so I don’t forget (it) at home”; the object is implied, understood from what was just said.

In casual speech, dropping его here is completely fine.

Why is it дома and not в доме or домой?

These forms express different ideas:

дома – adverb, means at home (location)
- не забыть его дома – not to forget it at home
в доме – “in the house”, more literal location inside some house (not necessarily your home)
- Would sound odd here; you are talking about not leaving the pass at home, not about some random house.
домой – direction, (to) home
- Used with verbs of motion: идти домой – “go home”, вернуться домой – “return home”.

So here дома is correct because it indicates the place where you risk leaving/forgetting the pass: at home.

How is класть conjugated? Кладу looks irregular.

Класть is indeed irregular. Present/future conjugation (imperfective):

я кладу – I put
ты кладёшь – you put
он/она кладёт – he/she puts
мы кладём – we put
вы кладёте – you (pl./formal) put
они кладут – they put

Past tense:

он клал, она клала, оно клалó, они клали

Imperative:

клади (ты) – put
кладите (вы) – put (pl./formal)

Perfective counterpart is положить:

я положу, ты положишь, они положат, etc.

Can I change the word order, for example: Я кладу в кошелёк проездной?

Yes, Russian word order is relatively flexible. These variants are all possible:

Я кладу проездной в кошелёк… (most neutral)
Я кладу в кошелёк проездной… (slightly more focus on в кошелёк)
Проездной я кладу в кошелёк… (emphasis on проездной)

The original Я кладу проездной в кошелёк is the most natural, neutral ordering. Changing it slightly can shift emphasis, but usually doesn’t change the basic meaning.

Do I have to say я, or can I just say Кладу проездной в кошелёк…?

You can omit я in context:

Кладу проездной в кошелёк, чтобы не забыть его дома.

Russian often drops the subject pronoun when:

the verb form clearly indicates the person (кладу can only be “I”),
and the subject is obvious from the situation.

Including я is completely correct and neutral; omitting it is also natural, especially in speech, notes, or informal writing.

How do you pronounce проездной, кошелёк, and where is the stress?

Stress and pronunciation:

проездной – stress on the last syllable: про-езд-ной → [pra-yezd-NÓY]
кошелёк – stress on ё: коше-лёк → [kasha-LYÓK]; ё is always stressed.
кладу – stress on у: кла-ду → [kla-DÚ]
дома – дОма in this meaning (at home), stress on the first syllable: [DÓ-ma].

Note: in everyday Russian spelling, ё is often written as е (кошелек), but it is still pronounced [ё].