Learn Hardcore Japanese: kyou ha keeki wo hitotu tabemasita.

Japanese often marks the topic with は, which may or may not be the same as the subject. English usually doesn’t mark topics explicitly, so this feels new to English speakers.

Why is there no explicit “I” in the Japanese sentence?

Japanese often omits pronouns like I, you, he, she when they’re clear from context.

In English, we must say I ate, but in Japanese, if it’s obvious who did the action, you just say:

食べました。
“(I) ate.” / “(We) ate.” — subject depends on context.

In this sentence, context (and default assumptions) make it clear the speaker is talking about themselves, so “I” is simply left out:

(私は) 今日はケーキを一つ食べました。

What does the particle を do in ケーキを?

を (pronounced お) is the direct object marker. It shows what the action is done to.

ケーキ = cake
ケーキを = cake as the thing being eaten

The structure is:

[Object] を [Verb]
ケーキを食べました。 = “(I) ate cake.”

So を marks ケーキ as the thing that is eaten.

Could I use が instead of を, like ケーキが一つ食べました?

No, ケーキが一つ食べました is ungrammatical in normal Japanese.

を marks the direct object of the verb (what is eaten).
が typically marks the subject (the doer/experiencer of the action).

If you say ケーキが食べました, it would mean “The cake ate (something)” — which is wrong semantically.

You need:

ケーキを食べました。 = “(I) ate cake.”
ケーキを一つ食べました。 = “(I) ate one (piece of) cake.”

What exactly is 一つ (ひとつ)? Why not just say 一?

一つ (ひとつ) is a number + counter word. Japanese doesn’t normally say bare numbers like 一 with nouns the way English says “one cake.”

Instead, it uses counters, which are special measure words.

一つ (ひとつ) = one (thing) – a generic counter for small, countable items
ケーキを一つ食べました。 = “(I) ate one (piece of) cake.”

Just 一 by itself is only the number “1” as a numeral; it’s not used alone in this way in a sentence. You need a counter like つ, 個 (こ), 枚 (まい), etc.

Are there more specific counters I could use instead of 一つ for cake?

Yes. 一つ is a generic counter, but you’ll also see:

一個 (いっこ) – one piece/one item (colloquial, often for small solid things)
一切れ (ひときれ) – one slice (if it’s a sliced cake)
一ホール – one whole cake (loanword usage: “one whole (cake)”)

So:

ケーキを一つ食べました。 – I ate one (cake / piece of cake).
ケーキを一切れ食べました。 – I ate one slice of cake.

一つ is safe and natural here, especially at a beginner level.

Why does 一つ come after ケーキ instead of before, like in English?

Japanese can place the number + counter either:

After the noun (very common in this kind of sentence):
- ケーキを一つ食べました。
  literally: cake-object one-counter ate
Before the noun (often in more descriptive noun phrases):
- 一つのケーキを食べました。

The most natural pattern when simply stating how many you ate/drank/etc. is:

[Noun] を [Number+Counter] [Verb]
→ ケーキを一つ食べました。

The [Number+Counter] の [Noun] pattern (e.g., 一つのケーキ) can be used, but in many everyday sentences it sounds a bit stiff or is less common than the first pattern.

Why is there no particle after 一つ?

The particle を is already attached to ケーキ, which functions as the full object phrase:

ケーキを一つ = “cake (object) – one (of it)”

In Japanese, the particle generally attaches to the last word of the noun phrase, but here the structure is:

ケーキを (object marker on the noun)
一つ (a quantifier describing how many of that noun)

So you don’t say ケーキを一つを — that would be like having two object markers. The single を on ケーキ is enough for the entire idea “one cake” as the object of 食べました.

What form is 食べました? How is it related to 食べる?

食べました is the polite past form of the verb 食べる (to eat).

Dictionary form: 食べる – “to eat” / “eat(s)”
Polite non-past: 食べます – “eat / will eat (polite)”
Polite past: 食べました – “ate (polite)”

Structure:

食べ – verb stem
ました – polite past ending

So the sentence is in the past tense and polite style.

What is the difference between 食べた and 食べました?

Both mean “ate”, but the politeness is different.

食べた – casual past
- Used with friends, family, people close to you.
食べました – polite past
- Used with strangers, teachers, colleagues, in formal situations.

So:

今日ケーキを一つ食べた。 – “I ate one piece of cake today.” (casual)
今日ケーキを一つ食べました。 – same meaning, but polite.

Why is the verb 食べました at the end of the sentence?

Japanese has a basic SOV (Subject–Object–Verb) word order:

Subject (often omitted)
Time/topic phrases
Object(s)
Verb at the end

So:

(私は) – (I) – omitted
今日は – as for today
ケーキを一つ – one cake (object)
食べました。 – ate

In Japanese, the main verb almost always comes at the end of the clause, unlike English SVO (Subject–Verb–Object).

Could I drop は and just say 今日ケーキを一つ食べました?

Yes, that sentence is grammatically fine and very natural:

今日ケーキを一つ食べました。

Without は, 今日 is just a time expression (“today”), not explicitly marked as the topic. In many everyday sentences, time expressions are often used without は.

Subtle nuance:

今日はケーキを一つ食べました。
→ Slightly emphasizes “as for today” (maybe in contrast to other days).
今日ケーキを一つ食べました。
→ More neutral: “I ate one piece of cake today.”

Both are correct; context and emphasis decide which feels better.

Is 今日 always read as きょう? I’ve seen こんにち too.

The kanji 今日 has more than one reading:

きょう – “today” (the everyday word)
こんにち – also written 今日, but this is a more formal/literary word meaning “nowadays” / “the present time,” as in 今日の日本 (こんにちのにほん) – “Japan today / contemporary Japan.”

In your sentence, 今日 meaning “today” (this day) is always read きょう.