Benim seni ne kadar takdir ettiğimi bilmiyor olabilirsin.

You may not know how much I appreciate you.

Breakdown of Benim seni ne kadar takdir ettiğimi bilmiyor olabilirsin.

• ben: I
• sen: you
• bilmek: to know
• olabilmek: to be able

Questions & Answers about Benim seni ne kadar takdir ettiğimi bilmiyor olabilirsin.

Why is it benim and not just ben at the beginning?

In this sentence, benim is in the genitive case and works as the subject of the embedded clause benim seni ne kadar takdir ettiğimi.

Turkish often uses this pattern for “that-clauses”:

• Benim geldiğimi biliyorsun.
  You know (that) I am coming.

Structure:

• benim = my / of me (genitive)
• geldiğimi = that I came / that I am coming (a verb turned into a noun-like form)

So:

• benim seni ne kadar takdir ettiğimi ≈ how much I appreciate you
  Literally: the my appreciating-you-how-much thing

ben would be the bare subject of a finite verb (ben geliyorum, ben biliyorum), but here the verb etmek is turned into a nominal form (ettiğimi), so its subject needs to be in genitive: benim.

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Is benim actually necessary here, or can I leave it out?

You can leave it out; the sentence is still grammatical and very natural:

• Seni ne kadar takdir ettiğimi bilmiyor olabilirsin.

In Turkish, the genitive subject of such clauses (the benim) is often omitted when it is clear from context who the subject is. The -im on ettiğimi already shows the subject is “I”.

So:

• With benim: slightly clearer, a bit more explicit.
• Without benim: more common in everyday speech, a bit more flowing.

Both are correct.

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Why is it and not ?