אני לא בטוח שזה המפתח שלך.

I am not sure that this is your key.

Breakdown of אני לא בטוח שזה המפתח שלך.

• זה: this
• אני: I
• לא: not
• ש: that
• שלך: your
• מפתח: key
• בטוח: sure

Questions & Answers about אני לא בטוח שזה המפתח שלך.

How do you pronounce אני לא בטוח שזה המפתח שלך?

A common transliteration is:

Ani lo batuaḥ she-ze ha-mafteaḥ shelkha / shelakh

A few pronunciation notes:

• אני = ani = I
• לא = lo = not
• בטוח = batuaḥ = sure
• שזה = she-ze = that this / that it is
• המפתח = ha-mafteaḥ = the key
• שלך:
  • shelkha if speaking to a man
  • shelakh if speaking to a woman

The sound ḥ represents the Hebrew letter ח, a throaty sound, like the ch in Scottish loch or German Bach.

Why is there no Hebrew word here for am or is?

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

So:

• אני לא בטוח literally looks like I not sure
• זה המפתח שלך literally looks like this the-key your

But in natural English, that becomes I’m not sure this is your key.

This is very normal in Hebrew. Compare:

• אני עייף = I am tired
• היא בבית = She is at home
• זה נכון = This is correct

In past and future, Hebrew usually does use a form of to be:

• לא הייתי בטוח = I wasn’t sure
• לא אהיה בטוח = I won’t be sure

What exactly does שזה mean?

שזה is made of two parts:

• ש־ = that
• זה = this / that / it

So שזה literally means something like that this is or that it is.

In this sentence:

• אני לא בטוח שזה המפתח שלך
• literally: I am not sure that this/it is the key of yours

In natural English, we usually say:

• I’m not sure this is your key
• or I’m not sure that’s your key

Also, ש־ is a prefix, so it attaches directly to the next word. That is why it is written as one word: שזה.

Why is it בטוח and not בטוחה?

Because בטוח is the masculine singular form.

Hebrew adjectives must agree with the person they describe. Here, בטוח describes the speaker, the I in אני.

So:

• if a man is speaking: אני לא בטוח
• if a woman is speaking: אני לא בטוחה

Other forms would be:

• אנחנו לא בטוחים = We’re not sure (masculine/mixed group)
• אנחנו לא בטוחות = We’re not sure (all-female group)

So the form of sure changes depending on who is speaking.

Why is לא placed before בטוח?

Because לא normally comes right before the thing being negated.

Here it negates בטוח:

• אני לא בטוח = I am not sure

This is the normal order:

• subject + לא + adjective / verb / phrase

Examples:

• אני לא רעב = I’m not hungry
• היא לא בבית = She isn’t at home
• אנחנו לא יודעים = We don’t know

So אני לא בטוח is the standard, natural order.

Why is it המפתח שלך and not מפתח שלך?

Because in Hebrew, when you use שלי / שלך / שלו / שלה and similar possessive forms, the noun is usually definite.

So:

• המפתח שלך = your key
• literally, something like the key of yours

This is the normal Hebrew pattern:

• הספר שלי = my book
• הבית שלה = her house
• הטלפון שלנו = our phone

For that reason, מפתח שלך would usually sound wrong or at least nonstandard in ordinary modern Hebrew.

What does זה mean here? Why is it זה?

Here זה functions as this / that / it.

In the clause:

• זה המפתח שלך

it means:

• this is your key
• or, depending on context, that is your key

Hebrew does not always match English exactly in the this/that distinction, especially in sentences like this.

It is זה because מפתח is a masculine singular noun. In standard Hebrew, זה is the masculine singular form.

If the noun were feminine, you would often use זאת or זו instead:

• זאת התיקייה שלך = This is your folder

Does שלך mean your when talking to a man or to a woman?

It can be either, depending on pronunciation.

In unpointed Hebrew, both are written the same way: שלך

But they are pronounced differently:

• שֶלְךָ = shelkha = your (to a man)
• שֶלָךְ = shelakh = your (to a woman)

So in normal Israeli spelling, you often cannot tell from writing alone whether the listener is male or female. You figure it out from:

• context
• speech
• vowel marks, if they are written

Could I say אני לא בטוח אם זה המפתח שלך instead?

Yes. That is also natural Hebrew.

Compare:

• אני לא בטוח שזה המפתח שלך
• אני לא בטוח אם זה המפתח שלך

Both can mean I’m not sure if this is your key.

A rough difference is:

• ש־ often introduces a statement-like clause: that...
• אם more clearly means if / whether

So אם can feel a little closer to English whether:

• I’m not sure whether this is your key

But in everyday Hebrew, לא בטוח ש־ is very common and natural.

Can אני be omitted?

Sometimes, yes.

You may hear:

• לא בטוח שזה המפתח שלך

This can mean:

• I’m not sure this is your key
• or more generally Not sure this is your key

That version is common in spoken Hebrew, especially when the subject is obvious from context.

Still, the full sentence:

• אני לא בטוח שזה המפתח שלך

is clearer and more complete, especially for learners and in neutral written Hebrew.

Is this sentence natural Hebrew, or would a native speaker say it differently?

Yes, it is natural Hebrew.

A native speaker could absolutely say:

• אני לא בטוח שזה המפתח שלך

Depending on context, they might also say slightly shorter versions, such as:

• לא בטוח שזה המפתח שלך
• אני לא בטוח שזה שלך — if it is already clear that it is a key
• אני לא בטוח אם זה המפתח שלך

But your original sentence is fully natural and idiomatic.