Παρεμπιπτόντως, βρήκα το βιβλίο σου.

Παρεμπιπτόντως means by the way or incidentally. It is used to introduce something additional, often something that is not the main point of the conversation.

In this sentence, it works just like English By the way, ...

It is a fairly formal or neutral-sounding word. In everyday speech, many speakers also use με την ευκαιρία or just other conversational transitions depending on context.

The comma is used because Παρεμπιπτόντως functions as a sentence adverb or discourse marker at the beginning of the sentence. It sets up the rest of the statement, much like in English:

By the way, I found your book.

So the comma helps separate the introductory word from the main clause.

Βρήκα is the first person singular form of the verb βρίσκω, meaning to find.

So:

• βρίσκω = I find / I am finding
• βρήκα = I found

This is the simple past form, often called the aorist in Greek grammar.

Because the sentence refers to a completed action in the past: I found your book.

Greek usually uses:

• βρίσκω for present or habitual meaning: I find / I am finding
• βρήκα for a single completed event in the past: I found

So βρήκα tells you the speaker found the book at some point, and that action is complete.

Το is the definite article, meaning the.

So:

• το βιβλίο = the book

Greek uses definite articles very often, including in places where English also uses the. Since the sentence means I found your book, Greek expresses that as I found the book your, with the possessive placed after the noun.

In Greek, weak possessive forms like μου, σου, του, της, μας, σας, τους usually come after the noun.

So:

• το βιβλίο σου = your book
• literally: the book your

This is the normal Greek pattern. English puts the possessive first, but Greek often puts it after the noun.

Σου is the weak genitive form of εσύ (you, singular).

Here it means your.

Compare:

• εσύ = you
• σου = your / to you

So το βιβλίο σου means your book, but σου can also mean to you in other sentences, depending on the structure.

Σου is singular: your when speaking to one person.

If you are speaking to more than one person, Greek uses σας:

• το βιβλίο σου = your book (one person)
• το βιβλίο σας = your book (more than one person, or formal singular)

Greek also uses σας as a polite/formal singular your, similar to formal you.

Greek nouns belong to grammatical genders: masculine, feminine, or neuter. Βιβλίο happens to be neuter, so it takes the neuter article το.

That is why you get:

• το βιβλίο = the book

Gender in Greek is a grammatical category, so it does not necessarily reflect anything natural about the object itself.

It is in the accusative case, because it is the direct object of βρήκα.

The speaker is doing the action of finding, and the book is what was found.

In this particular noun, βιβλίο, the nominative and accusative singular forms look the same:

• nominative: το βιβλίο
• accusative: το βιβλίο

So you understand its role from the sentence structure, not from a visible ending change.

A natural pronunciation would be approximately:

Pa-rem-bi-PTON-dos, VRI-ka to vi-VLI-o sou

A few notes:

• Παρεμπιπτόντως has the stress on -πτόν-
• βρήκα has the stress on βρή-
• βιβλίο has the stress on -βλί-
• σου sounds like soo

The β in Modern Greek sounds like v, not like the English b.

It is definitely correct and used, but it can sound a little more formal or polished than the most casual everyday speech.

In conversation, native speakers may still use it, especially in neutral or educated speech. But depending on the situation, they might also choose a simpler conversational equivalent.

So as a learner, it is good to recognize and use it, but also be aware that it is not the only way to say by the way.

Yes. Greek often omits subject pronouns because the verb ending already shows the subject.

So βρήκα already means I found. You do not need to say εγώ unless you want emphasis.

• Βρήκα το βιβλίο σου. = I found your book.
• Εγώ βρήκα το βιβλίο σου. = I found your book. / I was the one who found your book.

This is very common in Greek.