kazoku to yuusyoku wo tabemasita.

Here, と means with.

So 家族と means with (my) family.

In Japanese, と can have other meanings too, such as and, but in this sentence it is marking the person or group you did the action with.

を marks the direct object of the verb.

The verb 食べました means ate, so the thing being eaten is 夕食. That is why Japanese uses 夕食を.

So:

• 夕食 = dinner
• 夕食を食べました = ate dinner

Japanese often leaves out the topic or subject when it is already clear from context.

In English, you usually need a subject like I or we, but in Japanese it is very common to omit it.

So 家族と夕食を食べました。 can naturally mean:

• I ate dinner with my family.
• He ate dinner with his family.
• She ate dinner with her family.

The exact subject depends on the situation.

Japanese often leaves out words that are obvious from context.

With relationship words like 家族, 母, 父, and so on, the listener often understands whose family is being talked about without needing 私の.

So 家族と will often be understood as with my family if the speaker is talking about their own situation.

If you want to be extra clear, you can say 私の家族と.

食べました is the polite past form of 食べる, which means to eat.

Breakdown:

• 食べる = to eat
• 食べます = eat / will eat (polite)
• 食べました = ate (polite past)

So this sentence is in polite speech.
The plain past form would be 食べた.

Japanese normally puts the verb at the end.

That means a sentence like this often follows a pattern like:

• companion + と
• object + を
• verb

So:

• 家族と = with family
• 夕食を = dinner
• 食べました = ate

This is one of the biggest word-order differences between Japanese and English.

Yes, と can also mean and when it connects nouns.

For example:

• AとB = A and B

But in this sentence, と is understood as with because of the overall structure:

• 家族と = with family
• 夕食を食べました = ate dinner

The particle を makes it clear that 夕食 is the thing being eaten, so 家族と is not part of a simple noun list here.

No.

The particles prevent that meaning.

• 家族と = with family
• 夕食を = dinner as the object

If 家族 were also something being eaten, it would need a particle that marks it as an object, not と.

So the grammar clearly shows that the speaker ate dinner, and the family were companions in the action.

Although を is often written as wo in romanization charts, in modern Japanese it is usually pronounced o.

So:

• 夕食を食べました
• pronounced roughly as yuushoku o tabemashita

No. Normal Japanese is usually written without spaces.

So this sentence would normally be written as:

家族と夕食を食べました。

Spaces are often added in beginner materials to make the parts easier to see.

It could, but it is not necessary.

• 家族と夕食を食べました。 = I ate dinner with my family.
• 家族と一緒に夕食を食べました。 = I ate dinner together with my family.

Adding 一緒に makes the idea of together more explicit, but と by itself already works perfectly well for with here.

Yes, but the nuance changes a little.

• 家族と夕食を食べました focuses on with my family
• 家族で夕食を食べました treats the family as a group doing the action

So 家族で can feel more like we ate dinner as a family or the family ate dinner together, while 家族と sounds more like I ate dinner with my family.

Both are natural, but they are not exactly identical.