Learn Hardcore Japanese: mukasi no watasi ha nihongo ga zenzen wakarimasen desita. - In the past, I couldn’t understand Japanese at all.

In natural English we usually just say “In the past, I didn’t understand Japanese at all,” but Japanese can very naturally talk about “past me” as if it’s a slightly separate version of yourself.

Why is there a の between 昔 and 私?

の here links two nouns: 昔 (past) and 私 (I/me).

A pattern to remember is:

A の B → “B that is related to A”
- often “A’s B” or “B of A,” but sometimes more loosely “the B from/at/in A”

Some examples:

子供の私 – “me as a child / my childhood self”
学生の彼 – “him as a student / his student self”

So 昔の私 means “my self in the past / past me.” It’s not a possessive in the ownership sense, but it’s the same grammar.

Could I say 昔、私は日本語が全然分かりませんでした instead of 昔の私? What’s the difference?

Yes, you can say:

昔、私は日本語が全然分かりませんでした。

This sounds like:

“In the past, I didn’t understand Japanese at all.”

昔、私は… uses 昔 as a time adverb (“long ago, in the past”).
昔の私 focuses more on “the past version of me” as a character, almost contrasting with “the current me.”

Nuance:

昔、私は… – just places the time in the past.
昔の私は… – tends to contrast with 今の私は… (“now I do understand”), even if you don’t say that second part out loud.

Why does 私 have は, but 日本語 has が? Why not use は for both?

In 昔の私は日本語が全然分かりませんでした:

私は – topic: “As for me / speaking about me”
日本語が – subject of the verb 分かりません (“(I) don’t understand Japanese”)

は marks what you’re talking about (topic, theme).
が often marks what directly does/undergoes the verb, or what is being experienced in a verb like 分かる.

You could say 日本語は全然分かりませんでした, but that subtly shifts the focus:

日本語が分かりません – “I don’t understand Japanese (at all).” (neutral statement of fact)
日本語は分かりません – “(At least) Japanese, I don’t understand.” (contrast-y, like “Japanese, no; maybe other things yes”)

So using が with 日本語 is the most neutral and common pattern with 分かる.

What exactly is が doing after 日本語? Why not を?

The verb 分かる (wakaru) doesn’t take を; it takes が for the thing understood:

日本語が分かる – “(I) understand Japanese.”
意味が分かる – “(I) understand the meaning.”

This is just how 分かる works grammatically. It’s not “to understand (something) [direct object]” with を; instead it’s more like “(something) becomes clear to me,” and that “something” is marked with が.

Using 日本語を分かりません is unnatural in standard Japanese.

I learned that 全然 is used with negatives, like “not at all.” But I’ve heard 全然大丈夫 (“totally fine”). How does that work?

Traditionally:

全然 (zenzen) + negative ⇒ “not at all”
- 全然分かりません – “I don’t understand at all.”
- 全然食べません – “I don’t eat it at all.”

In modern casual speech, people also use 全然 with positives to mean “totally / completely / really”:

全然大丈夫！ – “Totally fine!”
全然いいよ。 – “Completely okay!”

So:

In textbooks / formal writing: 全然
- negative is the “correct” pattern.
In everyday speech: 全然
- positive is very common and natural, especially among younger speakers, but it’s casual.

How do you get from 分かる to 分かりませんでした? What are the steps?

Base verb: 分かる (wakaru) – plain present affirmative

Polite present affirmative:

Take the verb stem: 分かり
Add ます → 分かります – “(I) understand.”

Polite present negative:

Replace ます with ません → 分かりません – “(I) do not understand.”

Polite past negative:

Make ません past: ませんでした
→ 分かりませんでした – “(I) did not understand.”

So the pattern is:

分かる → 分かります → 分かりません → 分かりませんでした

Could I move the words around, like 私は昔、日本語が全然分かりませんでした? Is that still correct?

Yes, that is correct:

昔の私は日本語が全然分かりませんでした。
私は昔、日本語が全然分かりませんでした。
私は日本語が全然分かりませんでした、昔は。 (last one is more conversational/emphatic)

Japanese is relatively flexible with word order as long as the verb (分かりませんでした) comes at the end and particles stay attached to the right words.

Changing the order can slightly shift the emphasis:

Sentence-initial 昔の私は highlights “the past me.”
私は昔、… highlights “me,” then adds “in the past” as extra info.

Why use 分かりませんでした and not 知りませんでした or 話せませんでした?

These verbs express different things:

分かる – to understand / to make sense of
- 日本語が分かりませんでした。 – “I didn’t understand Japanese (what it meant / what people were saying).”
知る – to know (a fact / information)
- 日本語を知りませんでした。 – feels more like “I didn’t know about Japanese” or “I wasn’t familiar with Japanese” (less common in this sense).
話す – to speak
- 日本語が話せませんでした。 – “I couldn’t speak Japanese.”

So:

分かりませんでした focuses on understanding.
話せませんでした focuses on speaking ability.
知りませんでした doesn’t usually mean “I couldn’t use the language”; it’s more about not knowing some fact.

What is でした doing here? I thought でした is for nouns and adjectives, but this is a verb.

You’re seeing でした as part of the polite negative past form ませんでした.

Mechanism:

Polite negative: ません (not ます)
Past tense of です is でした
In the ます-system, past negative is formed as ませんでした

So:

分かります – present polite
分かりません – present polite negative
分かりませんでした – past polite negative

Even though the piece でした looks like “past of です,” here you can just memorize ませんでした as a single unit: “did not (verb), polite.”