In short

Everyday Hebrew says “my house” with two words — הבית שלי (ha-bayit sheli), the של construction of lesson 10. But Hebrew also has a tighter, one-word way: it welds the owner straight onto the noun as a suffix. הבית שלי becomes ביתי (beiti), “my-house”. This is the synthetic possessive — literary and formal in flavour, but not optional: for kinship terms and a whole set of fixed idioms it is the normal, expected form. שמי דוד (shmi David) “my name is David”, לדעתי (le-da’ati) “in my opinion”, אשתי (ishti) “my wife” — nobody says השם שלי דוד in these.

There are two suffix sets to keep apart, chosen by the shape of the noun, not the owner. A singular noun takes the ביתי/ביתך/ביתו family (beiti/beitcha/beito). A plural noun takes a different, longer family built on the construct base -ei-: ספריי/ספריך/ספריו (sfarai/sfarecha/sfarav, “my/your/his books”). Get the two crossed and you say something false: ספרו (sifro) is “his book”, ספריו (sfarav) is “his books”.

The rule

• The suffix replaces both the article and של. A suffixed noun already means “the X of mine”, so you do not add ה־ to it and you do not add של. “My house” is ביתי (beiti) — never הביתי, never ביתי שלי. Either say it synthetically (ביתי) or analytically (הבית שלי), but never both at once.

• Singular nouns take the ביתי-set. On a masculine singular noun the base often shifts its vowel (בית bayit → beit-) and the endings are ־י/־ך/־ו/־ה/־נו/־כם/־ם: ביתי (beiti), ביתך (beitcha / beitech), ביתו (beito), ביתה (beitah), ביתנו (beitenu), ביתכם (beitchem), ביתם (beitam). These are the very same suffixes you met on singular-base prepositions in lesson 17 — think לו (lo), and the possessive ־ו on a noun is the same ־ו.

• Plural nouns take the ספריי-set, on the construct -ei- base. A plural noun first goes into its construct form — ספרים (sfarim) → construct ספרי (sifrei-) — and the suffixes ride that: ספריי (sfarai), ספריך (sfarecha), ספריו (sfarav), ספריה (sfareha), ספריהם (sifreihem). This is exactly the plural-base prepositional set of lesson 17 (עליי/עליו/עליה, alai/alav/aleha) and the smichut base of lessons 23 and 52 — you already own the machinery.

• Read ־יו as -av, and mind the extra yod. ספריו is sfarav (“his books”), not “sfariyu”; אביו is aviv (“his father”). And that single yod is load-bearing: ספרו (sifro) = “his book” (singular noun + singular suffix), while ספריו (sfarav) = “his books” (plural noun + plural suffix). Never put the singular suffix on a plural meaning.

• Feminine ־ה shifts to ־ת before the suffix. A feminine noun in ־ה goes into its ־ת construct first: משפחה (mishpacha) → משפחתי (mishpachti) “my family”, משפחתו (mishpachto) “his family”; דעה (de’a, “opinion”) → דעתי (da’ati), giving the idiom לדעתי (le-da’ati) “in my opinion”. You cannot suffix the bare ־ה: משפחהי is impossible.

• Kinship terms and some idioms have irregular bases. A handful of very high-frequency words rebuild before the suffix: אישה (isha) → אשתי (ishti) “my wife”, אשתו (ishto) “his wife”; אב (av) → אבי (avi) “my father”, אביו (aviv) “his father”; אח (ach) → אחי (achi), אחיו (achiv); בן (ben) → בני (bni) “my son”, בנו (bno). The plural הורים (horim, “parents”) uses the plural set: הוריי (horai) “my parents”, הוריו (horav). These are precisely the words where the synthetic form is the everyday norm.

• A suffixed noun is definite, so its adjective takes ה־. Because ביתי already means “the house of mine”, an agreeing adjective behaves as after any definite noun (lesson 7): ביתי הגדול (beiti ha-gadol) “my big house”, with ה־ on the adjective. Drop the ה־ and ביתי גדול (beiti gadol) is no longer a phrase — it is a whole sentence, “my house is big”.

Forms & patterns

Singular-noun suffixes — on בית (bayit, “house”), base beit-:

Plural-noun suffixes — on ספרים (sfarim, “books”), construct base sifrei-:

Singular noun vs plural noun — the “his” trap (one yod changes the number):

Feminine ־ה→־ת shift and kinship / idiom irregulars (with the “my” and “his” cells):

Examples

Common mistakes

• ספרו (for “his books”) -> ספריו (sfarav) - ספרו (sifro) is “his book”, one book; “his books” needs the plural base with the extra yod, ספריו.
• ביתי שלי -> ביתי (beiti) - the suffix already means “my”; don’t double it with של. Say ביתי or הבית שלי, never both.
• הביתי -> ביתי (beiti) - a suffixed noun is already definite, so it takes no ה־ of its own.
• ביתי גדול (meaning “my big house”) -> ביתי הגדול (beiti ha-gadol) - the adjective on a definite noun needs ה־; without it, ביתי גדול is the sentence “my house is big”.
• משפחהי -> משפחתי (mishpachti) - a feminine ־ה becomes ־ת before the suffix.
• אבו (for “his father”) -> אביו (aviv) - “father” rebuilds on the base אבי־; “his father” is אביו, read aviv, not “avo”.

Tips

• Choose the set by the noun, not the owner: singular noun → ביתי-family; plural noun → ספריי-family. “His book” ספרו vs “his books” ספריו turns on that one yod.
• You already learned both suffix sets on prepositions (lesson 17): לו (lo) mirrors the singular ־ו, and עליו/עליה (alav/aleha) mirror the plural ספריו/ספריה. Same endings, new host.
• Read the ending ־יו as -av: ספריו = sfarav, אביו = aviv. It looks like “-iyu”; it is not.
• The ־ה→־ת feminine shift and the -ei- plural base are just smichut (lessons 23 / 52) at work — the noun goes into its construct form first, then takes the suffix.
• Register: the synthetic ביתי is literary/formal, and everyday speech leans on הבית שלי (lesson 10). But some words live almost only in the suffix — שמי, לדעתי, אשתי, בעלי, אחי — produce those with the suffix. Full diglossia is lesson 60.
• Keep definiteness in mind: no ה־ on the suffixed noun, but ה־ does go on any agreeing adjective — ביתי הגדול, ספריי החדשים.
• Kinship terms are the highest-yield place to drill this: אבי, אמי, אחי, אחותי, בני, בתי, אשתי, בעלי, הוריי. Memorise them as ready-made words.
• The unvocalized ־ך hides a m/f split: שמך is shimcha to a man but shmech to a woman, exactly as לך is lecha/lach (lesson 17).