tomodati wo settokusita.

説得した is the past plain form of the verb 説得する, which means to persuade or to convince.

It breaks down like this:

• 説得 = persuasion / convincing
• する = to do
• した = did

So:

• 説得する = to persuade
• 説得した = persuaded

This is a very common pattern in Japanese: a noun of Chinese origin + する becomes a verb.

Examples:

• 勉強する = to study
• 電話する = to call
• 説明する = to explain

を marks the direct object of the verb — in other words, the person or thing that receives the action.

In 友達を説得した, the friend is the one being persuaded.

So the structure is:

• 友達 = friend
• を = object marker
• 説得した = persuaded

This gives: (I/someone) persuaded a friend / my friend / the friend.

Even though English uses word order to show the object, Japanese uses particles like を.

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

So 友達を説得した could mean:

• I persuaded my friend
• He persuaded his friend
• She persuaded a friend
• They persuaded their friend

The exact subject depends on the situation.

This is very normal in Japanese. If the speaker and context already make the subject obvious, Japanese usually does not repeat it.

By itself, 友達 just means friend or friend(s). Japanese usually does not mark:

• a vs the
• my vs your vs his/her
• singular vs plural

So 友達を説得した could mean:

• I persuaded my friend
• I persuaded a friend
• I persuaded the friend
• I persuaded my friends

Context tells you which one is intended.

Yes. 友達 can mean either friend or friends, depending on context.

So:

• 友達を説得した can mean persuaded a/my friend
• It can also mean persuaded my friends

If Japanese speakers need to make the plural especially clear, they might use other words or context, but often they do not need to.

説得した is in the plain past form, so it is casual / neutral plain style.

A more polite version would be:

• 友達を説得しました。

Both mean the same thing, but the tone is different:

• 説得した = plain
• 説得しました = polite

The plain form is very common in:

• casual conversation
• diary style
• stories
• informal writing

It is very close, but it often has a slightly stronger feeling of convincing someone through reasoning or argument.

So 説得する is often used when someone was reluctant, and you managed to talk them into something.

Depending on context, it may be translated as:

• persuade
• convince
• talk someone into something

So 友達を説得した may feel a bit stronger than just casually influencing a friend.

Normally, Japanese is written without spaces.

So the natural written form is:

友達を説得した。

The spaced version:

友達　を　説得した。

is usually just for learners, to make the sentence easier to read and to show the particle clearly.

It is pronounced roughly like:

tomodachi o settoku shita

A few notes:

• 友達 = ともだち = tomodachi
• を is written wo, but in modern Japanese it is usually pronounced o
• 説得 = せっとく = settoku
• した = shita

So the whole sentence is:

tomodachi o settoku shita

The dictionary form is 説得する.

The sentence uses the past plain form 説得した, which comes from する changing to した.

So:

• dictionary form: 説得する
• past plain form: 説得した

This is useful because when you look up verbs in a dictionary, you usually look for the dictionary form.

Yes. In many contexts, convinced is a very natural translation.

説得した often overlaps with both:

• persuaded
• convinced

The best English choice depends on the context:

• If the focus is on getting the friend to do something, persuaded may fit better.
• If the focus is on changing the friend’s mind, convinced may fit better.

Without more context, either could be correct.

Japanese word order is more flexible than English, but the most neutral order here is:

友達を説得した。

Because を clearly marks 友達 as the object, Japanese can sometimes move things around for emphasis. However, with such a short sentence, this basic order is the most natural.

A key point is that particles matter more than English-style word order.

Not for the same meaning.

• 友達を説得した = persuaded the friend
• 友達は説得した would make friend the topic, not the object

So 友達は説得した sounds more like:

• As for my friend, (he/she) persuaded (someone)

That is a very different meaning.

This is a common learner mistake: は does not replace を when the noun is the direct object of the verb.