Learn Hardcore Japanese: watasi ha kazoku ni kansya no kimoti wo messeezi de tutaemasita. - I conveyed my feelings of gratitude to my family by message.

Because it is obvious from context who the subject is. は here does not mean “subject marker” in a strict grammatical sense; it mainly introduces what the sentence is about.

Why is 家族 marked with に and not を?

に here marks the recipient / target of the action.

家族に = to my family / toward my family

In this sentence:

The thing being conveyed is 感謝の気持ち → marked with を (direct object).
The person receiving that thing is 家族 → marked with に (indirect object / target).

So:

感謝の気持ちを伝える = to convey one’s feelings of gratitude
家族に感謝の気持ちを伝える = to convey one’s feelings of gratitude to one’s family

If you used 家族を, it would suggest that 家族 is the thing being conveyed (which makes no sense here).

What exactly does 感謝の気持ち mean, and why not just say 感謝?

感謝の気持ち literally means:

感謝 = gratitude / appreciation
〜の気持ち = the feeling(s) of 〜
→ 感謝の気持ち = the feeling(s) of gratitude / my grateful feelings

Why not just 感謝?

You can say 感謝を伝えました and it is grammatically correct and understandable. However:

感謝の気持ち sounds a bit softer, more emotional, and more natural in everyday speech.
感謝 alone can feel a little more abstract or formal (like the concept of gratitude).
感謝の気持ち emphasizes your personal feelings, not just the abstract idea of gratitude.

So:

家族に感謝を伝えました。 – I conveyed gratitude to my family. (OK, slightly more formal/abstract)
家族に感謝の気持ちを伝えました。 – I conveyed my feelings of gratitude to my family. (very natural, personal)

What is the role of の in 感謝の気持ち?

The の here is like the English “of” in a noun phrase:

感謝の気持ち
→ 感謝 (gratitude) の (of) 気持ち (feeling)
→ feeling of gratitude / grateful feeling

This is one common pattern:

Noun A ＋の＋ Noun B → Noun B of Noun A or Noun A-type Noun B

Other examples:

日本の文化 = culture of Japan / Japanese culture
子どもの本 = children’s book / book for children

So 感謝の気持ち is “the feeling that is a kind of 感謝” → feeling of gratitude.

Why does 感謝の気持ち take を?

を marks the direct object of the verb 伝える.

The verb:

伝える = to convey / to communicate / to tell (something)

What is being conveyed?

感謝の気持ち = feelings of gratitude

Therefore:

感謝の気持ちを伝える = to convey (one’s) feelings of gratitude.

So the structure is:

[Direct object] を [伝える]
→ 感謝の気持ちを伝える = convey feelings of gratitude
→ In the full sentence: 家族に感謝の気持ちをメッセージで伝えました。

What does メッセージで mean? What does で do here?

メッセージで uses で to mark the means / method of doing something.

メッセージ = a message (often a text message, chat, email, etc.)
〜で (in this use) = by / via / through (as a means)

So:

メッセージで伝えました。 = I conveyed it by message / via a message.

This “means / instrument” use of で is very common:

バスで行きます。 = I’ll go by bus.
日本語で話します。 = I’ll speak in Japanese.
メールで知らせます。 = I’ll inform you by email.

In your sentence, メッセージで tells us how the feelings were conveyed: via a message.

Can I change the word order, like メッセージで家族に感謝の気持ちを伝えました? Is that still correct?

Yes, that is still correct and natural.

Japanese word order is relatively flexible as long as:

The verb stays at the end, and
Particles clearly show each word’s role.

All of the following are possible and natural (with slightly different emphasis):

家族に感謝の気持ちをメッセージで伝えました。
家族にメッセージで感謝の気持ちを伝えました。
メッセージで家族に感謝の気持ちを伝えました。

The basic pattern is:

[Recipient に] [Object を] [Means で] [Verb]

Reordering the non-verb parts usually changes rhythm or emphasis, not the core meaning, because に, を, and で clearly mark their functions.

Is 家族 singular or plural? Does this mean “to a family” or “to my family”?

家族 in Japanese is generally a collective noun meaning family as a group; it doesn’t explicitly mark singular vs plural the way English does.

In this sentence, context strongly suggests:

家族 = my family

Reasons:

Japanese often omits possessives like 私の when it is obvious whose something is.
Talking about “conveying feelings of gratitude” to family is usually about one’s own family unless otherwise specified.

So:

Literal: “(I) conveyed feelings of gratitude to family by message.”
Natural English: “I conveyed my feelings of gratitude to my family by message.”

If you really needed to specify someone else’s family, you could say for example:

友だちの家族に感謝の気持ちを伝えました。
= I conveyed my feelings of gratitude to my friend’s family.

Why is 私 included? Would it be more natural to omit it?

Yes, in many real-life contexts, 私 would be omitted:

家族に感謝の気持ちをメッセージで伝えました。

This is because:

Japanese often drops the subject when it is clear from context.
Saying 私 all the time sounds unnatural in casual or even standard conversation.

Including 私:

Is useful in textbooks and beginner materials to show the structure clearly.
May be used if you specifically want to contrast yourself with someone else (e.g., 私は did X, but 弟は did Y).

In a neutral sentence like this, most native speakers would leave 私 out unless there is a reason to stress “I, as opposed to others”.

What nuance does 伝えました have compared to verbs like 言いました or 話しました?

The verb 伝える means:

to convey, to communicate, to pass on (a message, information, thoughts, feelings).

Nuance:

言う = to say (specific words)
話す = to speak / to talk (often more about talking itself)
伝える = to convey or communicate something to someone (focus on the content being passed along)

So:

感謝の気持ちを言いました。 – “I said my feelings of gratitude.” (a bit odd; people don’t usually say it this way)
感謝の気持ちを話しました。 – “I talked about my feelings of gratitude.” (could work, but feels like you gave a talk about them)
感謝の気持ちを伝えました。 – “I conveyed my feelings of gratitude.” (most natural here)

伝える is commonly used for:

Messages: メッセージを伝える – convey a message
Information: 予定を伝える – let someone know the schedule
Feelings: 気持ちを伝える – convey your feelings

What does 〜ました add compared to 伝えた?

伝えました is the polite past form; 伝えた is the plain past form.

伝える → 伝えた (plain past)
伝える → 伝えます → 伝えました (polite past)

Differences:

伝えました
- Polite, used in normal conversations with people you are not very close to, in business, etc.
- Matches the usual です／ます style.
伝えた
- Casual, used with friends, family, people of equal or lower status in informal settings.
- Matches the だ／plain style.

So your sentence in casual speech might become:

家族に感謝の気持ちをメッセージで伝えた。

Could I say 家族に感謝しています instead? How is that different?

Yes, but the meaning and focus are a bit different.

家族に感謝しています。
= I am grateful to my family. / I appreciate my family.
- Focuses on your current emotional state (you are grateful now).
- Uses the verb 感謝する (“to be grateful / to appreciate”).
家族に感謝の気持ちをメッセージで伝えました。
= I conveyed my feelings of gratitude to my family by message.
- Focuses on the action you took in the past (you sent a message, you communicated it).

So:

Say 感謝しています when you want to state your gratitude.
Say 感謝の気持ちを伝えました when you want to describe how you expressed that gratitude to someone.

Why is メッセージ written in katakana? Could it be written some other way?

メッセージ is written in katakana because:

It is a loanword from English (message).
Loanwords and foreign-origin words are normally written in katakana.

In modern Japanese, メッセージ in katakana is the standard way to write it. There are native or Sino-Japanese words that can sometimes be used instead, depending on nuance, for example:

伝言（でんごん） – a message (often a short message passed on through someone)
メッセージ – is broader, and commonly used for:
- Text messages, chat messages, SNS messages, email messages, etc.

For your sentence, メッセージ in katakana is the natural and expected spelling.