היא נראית שמחה, אבל אני יודעת שהיא עייפה.

Here נראית means looks or seems/appears.

So היא נראית שמחה means She looks happy or She seems happy.

The verb comes from להיראות, which often means to appear / to look. In other contexts, it can also have a more literal sense like to be seen, but in this sentence, with an adjective after it, the natural meaning is looks/seems.

Because the subject is היא — she.

In Hebrew, verbs in the present tense and adjectives usually agree with the subject in gender and number.

So with a feminine singular subject:

• היא נראית
• היא שמחה
• היא עייפה

If the subject were masculine singular, you would get:

• הוא נראה
• הוא שמח
• הוא עייף

Because יודעת is the feminine singular form, so it tells us the speaker is female.

Hebrew present-tense forms show gender, so:

• אני יודעת = I know said by a female speaker
• אני יודע = I know said by a male speaker

So this sentence is being said by a woman or girl.

The ש־ means that.

So:

• אני יודעת שהיא עייפה = I know that she is tired

In Hebrew, ש־ is usually attached directly to the next word, so שהיא is literally that + she.

This is very common after verbs like:

• יודע/יודעת = know
• חושב/חושבת = think
• אומר/אומרת = say

Because in Hebrew, the present tense of to be is usually omitted.

So:

• היא עייפה literally looks like she tired
• but it means she is tired

This is normal Hebrew grammar.

You do use forms of to be in past and future, for example:

• היא הייתה עייפה = she was tired
• היא תהיה עייפה = she will be tired

But in the present, Hebrew usually leaves is/am/are out.

In this sentence, they are important for clarity.

A key thing to know is that Hebrew present tense does not mark person clearly the way English does. It mainly marks gender and number.

For example, יודעת can mean:

• I know (female)
• you know (female)
• she knows

So אני helps make it clear that the subject is I.

The same idea applies to היא עייפה. The word עייפה only tells you feminine singular, not whether the subject is I, you, or she. So היא is needed to show that it means she is tired.

In conversation, pronouns can sometimes be dropped if the context is obvious, but in a standalone sentence like this, keeping them is the normal and clearest choice.

Not necessarily.

נראית שמחה means she looks happy or she seems happy — it describes appearance, not a guaranteed fact.

That is exactly why the second half of the sentence is interesting:

• She looks happy
• but I know she is tired

So the sentence sets up a contrast between how she appears and what the speaker knows about her actual condition.

Also, being tired and looking happy are not impossible together — she may be smiling, but exhausted.

Only יודעת would change to יודע:

היא נראית שמחה, אבל אני יודע שהיא עייפה.

Everything else stays the same, because she is still feminine.

So:

• female speaker: אני יודעת
• male speaker: אני יודע

Then the feminine forms referring to she would become masculine:

הוא נראה שמח, אבל אני יודעת שהוא עייף.

That means:

He looks happy, but I know he is tired.

The changes are:

• היא → הוא
• נראית → נראה
• שמחה → שמח
• שהיא → שהוא
• עייפה → עייף

If the speaker were also male, then יודעת would become יודע too.