Learn Hardcore Japanese: kyou ha sukosi tukarete iru ki ga simasu.

Japanese often starts with a topic, not necessarily the subject, and then makes a comment about it. Here, today is the thing we’re talking about, and the comment is that (I) feel a bit tired today.

Without は, just 今日 at the beginning would feel incomplete or would need another particle (like 今日、 as just a time expression attached to the rest of the sentence).

Why is it 疲れている and not 疲れた?

疲れる is a verb meaning “to get tired / to become tired.”

疲れた is the past form:
- 疲れた = “I got tired” / “I became tired.”
疲れている is the te-form + いる, which often expresses a resulting state:
- 疲れている = “(I) am tired” (state that resulted from getting tired)

So:

今日は少し疲れた。
→ Focuses on the event: “I got a bit tired today.”
今日は少し疲れている。
→ Focuses on the current condition: “I am a bit tired today.”

In your sentence, the meaning is about your current state, so 疲れている is more natural.

What does 気がします mean? How should I understand this phrase?

気がします is a set expression that means something like:

“I feel (that) …”
“I have a feeling (that) …”
“It seems to me (that) …”

The literal pieces are:

気 – “feeling,” “mood,” “sense,” “mind”
が – subject marker
します – “to do”

So literally: “(a) feeling does (arises)”, but in natural English it’s “I feel that … / It feels like …”.

疲れている気がします = “I feel like I’m tired” / “I get the feeling that I’m tired.”

This softens the statement and makes it less direct, more tentative than just saying 疲れています (“I am tired”).

Why is the sentence 気がします at the end, not 気です?

気がします and 気です are different patterns.

気がする / 気がします is a fixed expression meaning
“to feel / to have a feeling / it seems (to me).”
気です would mean something like “is a feeling/spirit” and does not have this “I feel that…” meaning.

Examples:

疲れている気がします。
→ “I feel like I’m tired.”
これは変な気です。
→ “This is a strange feeling.” (here 気 is a noun being described)

In your sentence you’re not saying “It is a tired feeling.”
You’re saying “I feel (that) I am tired,” so you need 気がします, not 気です.

Who is the subject here? There is no “I” in the Japanese sentence, so how do we know it means “I feel a bit tired today”?

Japanese very often omits the subject when it is obvious from context.

In 今日は少し疲れている気がします, the most natural subject is the speaker:

“(I) feel that (I’m) a bit tired today.”

Why?

It’s talking about internal feelings/state (疲れている, “being tired”), which usually refers to oneself if not otherwise specified.
The verb 気がします (“I feel / it feels to me”) is typically about the speaker unless context says someone else is doing the feeling.

You could say it explicitly as:

今日は私は少し疲れている気がします。

But that sounds heavy and unnatural in casual conversation. Dropping 私 is normal.

What’s the difference between 今日は少し疲れています and 今日は少し疲れている気がします?

Both can be translated as something like “I’m a little tired today,” but the nuance is different:

今日は少し疲れています。
- Direct statement of fact: “I’m a bit tired today.”
- Sounds more certain, straightforward.
今日は少し疲れている気がします。
- Literally: “I feel like I’m a bit tired today.”
- Softer, more tentative, a bit like:
  - “I think I might be a bit tired today.”
  - “I kinda feel I’m a bit tired today.”

Using 〜気がします is a way to make your statement sound less blunt and more like a personal impression or reflection.

Why is が used after 気? Why not 気はします or 気をします?

Here 気 is the subject of the verb します in the expression 気がします.

気がする / 気がします = “to feel / to have a feeling”

Some patterns:

〜ような気がする – “to feel as if ~”
〜気がする – “to feel that ~”

気はします could exist, but it would mark 気 as a contrastive topic, which would be unusual here and would change the nuance.
気をします is not a normal pattern for this meaning.

So in this expression, が is the normal particle:

気がする = “a feeling arises / I get a feeling” → “I feel (that) …”

Why is there no particle after 少し? Can we say 少しは疲れている気がします?

In 今日は少し疲れている気がします, 少し is an adverb meaning “a little / a bit,” modifying 疲れている:

少し + 疲れている = “(am) a little tired”

Adverbs usually don’t take particles, so no particle is needed here.

You can say 少しは疲れている気がします, but the nuance changes:

少しは adds a sense of contrast/emphasis:
- “At least a little, I do feel tired.”
- “I do feel tired, at least a bit (even if not completely exhausted).”

In neutral, everyday speech, 今日は少し疲れている気がします without a particle after 少し is the most natural.

What’s the difference between 少し and ちょっと here? Could I say 今日はちょっと疲れている気がします?

Yes, you can say:

今日はちょっと疲れている気がします。

The difference is mainly nuance/register:

少し
- Slightly more neutral / textbook / formal.
- Common in writing and polite speech.
ちょっと
- Very common in casual conversation.
- Can sound a bit softer or more colloquial.
- Sometimes used to hedge or downplay things.

In this particular sentence, both are fine:

今日は少し疲れている気がします。
→ Polite, slightly “standard” feel.
今日はちょっと疲れている気がします。
→ Polite but a bit more conversational.

Is 疲れている present continuous, like English “am getting tired,” or is it more like “am tired”?

疲れている here expresses a state, not an ongoing action.

The pattern verb-te + いる can mean:

Ongoing action (like English progressive)
- 読んでいる = “am reading”
Resulting state (after something has happened)
- 疲れている = “(am) tired” (state after becoming tired)
- 結婚している = “(am) married” (state after getting married)
- 壊れている = “(is) broken” (state after being broken)

疲れる = “to get tired / become tired,” so 疲れている is the resulting state:
→ best translated as “am tired”, not “am getting tired.”

Is this sentence polite or casual? How would I say it more casual or more formal?

今日は少し疲れている気がします。 uses します, so it is polite (standard polite form).

More casual:
- 今日は少し疲れている気がする。
  (Change します → する)
- Or drop 気がする for a direct statement:
  - 今日は少し疲れてる。 (spoken contraction of 疲れている)
More formal / softer:
- 今日は少し疲れている気がいたします。
  (いたします is the humble form of します; very polite, businesslike)
- Or:
  - 今日は少し疲れているような気がします。
    (“I feel as if I might be a little tired today.” – adds softening with ような)

Could I say 今日は少し疲れた気がします? How is that different from 疲れている気がします?

Yes, you can say 今日は少し疲れた気がします, but the nuance is different.

疲れている気がします
- Focus on the current state:
  “I feel (that) I am a bit tired now.”
疲れた気がします
- 疲れた is “got tired / became tired” (past event).
- So this is more like:
  - “I feel like I got a bit tired today.”
  - “I feel as if I’ve gotten a bit tired.”

Use 疲れた気がします when you’re reflecting on the fact that you have become tired, maybe after some activity.
Use 疲れている気がします when you’re focusing on your present tired condition.