Learn Hardcore Turkish: O, bizim bu projeyi birlikte bitireceğimizi biliyor. - He knows that we will finish this project together.

In this sentence, context will tell you whether it’s “he” or “she”.
You can omit it:
Bizim bu projeyi birlikte bitireceğimizi biliyor.
still means “He/She knows that we will finish this project together.”
Using O just makes the subject explicit or slightly emphasized; in neutral everyday speech, people often drop it when it’s clear from context.

Why is it bizim, not biz? Why can’t we say “biz bu projeyi birlikte bitireceğimizi biliyor”?

In Turkish, when you have a subordinate clause used like a noun (e.g. “that we will finish…”), its subject must normally be in the genitive form.

biz = we
bizim = our

In bizim bu projeyi birlikte bitireceğimizi, the subject of the subordinate clause “that we will finish this project together” is bizim (“our”), not biz. This is the standard pattern:

bizim gelmemiz = our coming / that we come
senin söylemen = your saying / that you say
onların yardım etmesi = their helping / that they help

So biz in front of bitireceğimizi would be ungrammatical here; you need bizim.

Can we drop bizim and still keep the same meaning?

Yes. You can say:

Bu projeyi birlikte bitireceğimizi biliyor.

The -imiz part in bitireceğimizi already shows that the subject of the subordinate clause is “we”, so bizim can be omitted when the subject is clear.

Nuance:

With bizim: a bit more explicit or contrastive, like “that we (in particular) will finish this project together.”
Without bizim: more neutral and slightly shorter.

What exactly is inside the long form bitireceğimizi?

bitireceğimizi is made of several parts:

bitir- = root “to finish” (causative of bitmek “to end”)
-ecek → -eceğ- = future marker “will”
- Before a vowel, the final k of -ecek softens to ğ: bitirecek → bitireceğ-
-imiz → -imiz / -ımız etc. (here: -imiz) = 1st person plural possessive “our”
- So bitireceğimiz = “(that) we will finish” / “our finishing”
-i = accusative case ending

So:

bitir-eceğ-imiz-i = “our act of finishing (it)” in the accusative → “that we will finish (it)”

Compare:

bitireceğiz = we will finish
bitireceğimiz = that we will finish / our finishing
bitireceğimizi = (accusative) that we will finish (as the object of another verb, here biliyor)

Why does bitireceğimizi have the -i accusative ending? Isn’t biliyor already a verb?

Yes, biliyor is the main verb, and it needs an object (something that is known):

Neyi biliyor? – What does he/she know?
→ bizim bu projeyi birlikte bitireceğimizi – that we will finish this project together

To let this whole clause act as a direct object, Turkish turns the verb into a nominalized form and puts it in the accusative:

bitireceğimiz = that we will finish / our finishing
bitireceğimizi = that we will finish (object of biliyor)

So the -i on bitireceğimizi is there because the whole subordinate clause is the thing known.

Why is projeyi also in the accusative? Isn’t that “double accusative” a problem?

No problem; they have different roles:

projeyi (proje + -yi) = “the project” in accusative
→ object of the embedded verb bitireceğimiz (what we will finish)
bitireceğimizi (already in accusative)
→ the whole clause is the object of biliyor

So structurally:

O [bizim [bu projeyi] birlikte bitireceğimizi] biliyor.
- bu projeyi: object of “finish”
- bizim … bitireceğimizi: clause functioning as object of “know”

This kind of “nested” accusative marking is normal with embedded clauses in Turkish.

Where is the word “that” in this Turkish sentence?

Turkish usually doesn’t use a separate word for “that” in this kind of clause. Instead, it:

Nominalizes the verb, and
Marks the subject in genitive (often), and the whole clause in accusative if needed.

So:

O, bizim bu projeyi birlikte bitireceğimizi biliyor.
≈ “He/She knows that we will finish this project together.”

The “that” idea is carried by the form bitireceğimizi, not by a separate word. A literal-ish structural gloss:

bizim – our (subject of the subordinate clause, genitive)
bu projeyi birlikte bitireceğimiz – our finishing this project together
-i on bitireceğimiz – accusative, making the whole thing “what he/she knows”

Why is the order “bizim bu projeyi birlikte bitireceğimizi” and not closer to English order?

Turkish is generally SOV (Subject–Object–Verb) and puts the verb at the end of each clause, including subordinate ones. So inside the clause “that we will finish this project together”:

Subject (genitive): bizim
Object: bu projeyi
Adverb: birlikte (“together”)
Verb (nominalized): bitireceğimizi

So the order:

bizim (our / we)
bu projeyi (this project)
birlikte (together)
bitireceğimizi (that we will finish)

You can move birlikte a bit (e.g. bizim birlikte bu projeyi bitireceğimizi) to change emphasis, but the verb of the clause (bitireceğimizi) almost always stays last.

Why is it biliyor and not bilir or bildi?

All three forms are correct Turkish, but they express different time/aspect nuances:

biliyor (present continuous / stative)
→ “he/she knows (now)” – current state of knowing
- O, bizim bu projeyi birlikte bitireceğimizi biliyor.
  = He/She knows (is aware) that we will finish this project together.
bilir (aorist)
→ general knowledge, habitual, or “would know” in some contexts
- O, bizim bu projeyi birlikte bitireceğimizi bilir.
  = He/She (generally) knows / would know that we will finish this project together.
  Sounds more like a statement of fact or character.
bildi (simple past)
→ “he/she found out / came to know” (at some point in the past)
- O, bizim bu projeyi birlikte bitireceğimizi bildi.
  = He/She learned / realized that we will finish this project together.

In your sentence, biliyor is the most natural for “He/She knows that …” as a current fact.

Could we say “O biliyor ki bu projeyi birlikte bitireceğiz” instead? Is it the same meaning?

Yes, you can say:

O biliyor ki bu projeyi birlikte bitireceğiz.

This is also natural and means essentially the same: “He/She knows that we will finish this project together.”

Differences:

Original sentence (nominalized clause):
O, bizim bu projeyi birlikte bitireceğimizi biliyor.
- More formal/neutral, very typical of written Turkish.
- Uses the “genitive + nominalized verb” structure.
With ki:
O biliyor ki bu projeyi birlikte bitireceğiz.
- Slightly more colloquial / emphatic; ki works like a conjunction “that”.
- The subordinate clause after ki is in normal finite form (bitireceğiz), not nominalized.

Both are correct; choice depends on style and emphasis.

What is the difference between birlikte and beraber here? Can I replace one with the other?

In this sentence, birlikte and beraber are almost interchangeable:

O, bizim bu projeyi birlikte bitireceğimizi biliyor.
O, bizim bu projeyi beraber bitireceğimizi biliyor.

Both mean “together”.

Nuances (often subtle and context‑dependent):

birlikte
- Slightly more neutral and common in many contexts.
- Feels a bit more “formal” or standard in some styles.
beraber
- Very common in everyday spoken Turkish.
- Sometimes feels a bit more colloquial.

Functionally, learners can treat them as synonyms meaning “together” in sentences like this.