English that covers a startling amount of ground — I said that he left, the man that I met, so tired that I fell asleep — and English speakers arrive expecting one Hebrew word to do the same. Three do the job instead, and they are not interchangeable in the same way. ש־ is a prefix and the default for almost everything. כי is because, and also a complementiser in one specific register. אשר is the relative that formal writing still reaches for. The extended treatment of each is on ש־, כי and אשר; this page is the choice.
ש־ is a prefix, and that is the first thing to internalise
It is not a little word standing next to the clause — it is glued to the first word of it, exactly like ה־ or ב־. שהוא, שאני, שגר, שרציתי. There is never a space, and the ש never stands alone.
אמרתי לך שאני לא בא, למה אתה עוד שואל?
amárti lekhá she'aní lo ba, láma atá od sho'él?
I told you I'm not coming — why do you keep asking? (to a man)
השכן שגר למעלה מנגן בתופים בשתיים בלילה.
hashakhén shegár lemála menagén betupím bishtáyim baláyla
The neighbour who lives upstairs plays the drums at two in the morning.
Those two sentences show the whole range of ש־ in one page: the first is a complementiser (that I'm not coming), the second a relativiser (who lives upstairs). One prefix, both jobs, every register.
כי is two words wearing one spelling
Milog gives it two senses, and learners meet only the first.
Sense 1 — causal. Glossed מפני ש; מכיון; בגלל. This is the כי everybody learns and it is the everyday word for because.
לא הלכתי כי לא היה לי כוח.
lo halákhti ki lo hayá li kóakh
I didn't go because I couldn't be bothered.
Sense 2 — complementiser. Glossed by Milog simply as ש־, and illustrated with the biblical וירא אלוהים כי טוב. This is the sense that gets marked wrong on learners' work and should not be: אמר כי is standard formal and journalistic Hebrew, not an error and not archaic.
דובר המשטרה מסר כי החקירה נמשכת.
dovér hamishtará masár ki hakhakirá nimshékhet
The police spokesman said the investigation is ongoing. (formal/journalistic)
הוא אמר לי שהוא כבר בדרך, ואני עוד מחכה.
hu amár li shehú kvar badérekh, va'aní od mekhaké
He told me he was already on his way, and here I am still waiting. (the everyday twin)
Where the complementiser כי actually lives — measured
The useful question is not is כי allowed but after which verbs. Counting Hebrew Wikipedia's article namespace with insource:/…/ on 16 August 2026, each search run twice, and each pattern written with a leading space so that נאמר and ואמר are not swept in:
| Frame | with כי | with ש־ |
|---|---|---|
| after a reporting verb — אמר כי הוא amár ki hu against אמר שהוא amár shehú | 342 · 357 | 899 · 784 |
| after a volitional verb — רוצה כי rotsé ki against רוצה שהוא rotsé shehú | 7 | 68 |
Read the two rows against each other, because the contrast is the finding. After a reporting verb, כי carries something like a third of all the that-clauses in this written corpus — a live, ordinary choice. After a volitional verb it very nearly vanishes: seven hits in the whole encyclopedia. Reading all seven, two are the causal כי (doesn't want to, because he hopes…), three are translated or quoted older text (a rendering of Locke, a translated wartime diary, a 1930s quotation), and the remaining two are the encyclopedia's own formal narration.
So כי is not a general-purpose that. It is a reporting complementiser, at home after אמר, מסר, הודיע, טען and ביקש — the last of which returns 82 against roughly 790 for ביקש ש־, so ש־ leads there too, and by a wider margin than after אמר — and out of place after רוצה. That is a register-and-collocation fact rather than a rule of grammar; those five volitional hits show the door is not locked. But it tells you where to use it and where not to.
insource: figure is a floor, not a count. That is why the argument is built on the ratio and on the contrast between the two rows, both of which survive the drift.אשר: a style choice, not a fourth function
Milog defines אֲשֶׁר as מילת זיקה המקשרת משפט לוואי לשם עצם או לכינוי שקדם לה — a relative word linking an attributive clause to the noun before it — and its examples are זה בדיוק הדבר אשר אמרתי and אלה הילדים אשר נשלחו למנהלת. Rewrite either with ש־ and nothing changes but the register. אשר adds no function that ש־ lacks.
Milog has no register field, and where it does state a register it does so inside the gloss — its ברם entry opens מילת קישור ספרותית. It says nothing of the kind about אשר, so the literary standing of אשר has to be shown by where it turns up rather than asserted. One clean piece of evidence: the Academy of the Hebrew Language's own כללי הפיסוק (2017 edition, read from a Wayback snapshot of 31 December 2024) has a whole section on punctuating relative clauses, and every example in it is written with ש־. The string אשר occurs eight times in the entire document — six of them are כאשר, one is אשריך, and exactly one is a relative אשר, inside a quoted aphorism (מי אשר איננו יודע לכזב, איננו יודע אמת מהי). A rulebook writing its own examples reaches for ש־; אשר turns up when something is being quoted.
התנאים אשר נקבעו בהסכם אינם ניתנים לשינוי.
hatna'ím ashér nikbe'ú bahéskem einám nitaním leshinúy
The terms laid down in the agreement cannot be altered. (formal written — a contract, a ruling, a letter from an authority)
התנאים שסיכמנו כבר לא תקפים, הכול השתנה מאז.
hatna'ím shesikámnu kvar lo tkefím, hakól hishtaná me'áz
The terms we agreed aren't valid any more, everything's changed since. (the same construction, everyday register)
Two footnotes on אשר that matter more than the register point. First, the frozen compounds are not optional: באשר ל־ "as regards" and אשר על כן "therefore" have no ש־ twin at all — there is no *בש ל־ to fall back on. (כאשר looks like a counterexample and is not one: it does have a twin, and the twin is the everyday כש־.) Second, do not assume every since-word carrying a ש־ belongs to this family. מאחר ש־ does not: Milog lists it on the מאחר page, among the entries of the root אח״ר, late, after. The אשר entry's own compounds are יען אשר, עקב אשר and תחת אשר, all of them (literary).
באשר לתקציב, ההחלטה תתקבל רק בחודש הבא.
ba'ashér lataktsív, hahakhlatá titkabél rak bakhódesh habá
As regards the budget, the decision will only be taken next month. (formal — and this one has no everyday twin to swap in)
The procedure
Ask what the clause is answering.
| The clause answers… | Use | Register |
|---|---|---|
| what did he say / think / know | ש־ | neutral — every register |
| the same, in a newspaper or a report | כי | (formal) · (academic) — reporting verbs only |
| why | כי | neutral — every register |
| which one (relative clause) | ש־ | neutral — every register |
| the same, in careful writing | אשר | (formal) · (literary) |
The short version: ש־ is never wrong. כי and אשר are both things you add on purpose.
Common Mistakes
1. Writing ש־ with a space after it. The most visible learner error in written Hebrew, and it comes from thinking of ש as a word.
❌ אני חושב ש הוא צודק
Incorrect as a spelling — ש־ is a prefix and is written joined to the next word, with no space: שהוא. The same goes for כש־, מש־ and ל־, ב־, כ־, ה־.
אני חושב שהוא צודק, פשוט קשה לי להודות בזה.
aní khoshév shehú tsodék, pashút kashé li lehodót bazé
I think he's right, I just find it hard to admit it. (m. speaker)
2. Leaving it out altogether. English lets you drop that — I think he's late, the man I met — and Hebrew never does. Both the complementiser and the relativiser are compulsory.
❌ אני חושבת הוא לא יבוא
Incorrect — Hebrew has no bare-complement option: the ש־ is compulsory. אני חושבת שהוא לא יבוא. The same applies to relatives — 'the man I met' is האיש שפגשתי, never האיש פגשתי.
אני חושבת שהוא לא יבוא, הוא לא ענה לאף הודעה.
aní khoshévet shehú lo yavó, hu lo aná le'áf hoda'á
I don't think he's coming — he hasn't answered a single message. (f. speaker)
3. Using כי to introduce a relative clause. Once כי = that is in your head, it wants to do the relative's job too. It cannot: כי never attaches to a noun.
❌ המסעדה כי אהבנו נסגרה בשנה שעברה
Incorrect — כי links a clause to a whole sentence, never to a noun. A relative clause takes ש־ (or, in formal writing, אשר): המסעדה שאהבנו.
המסעדה שאהבנו נסגרה בשנה שעברה ומאז לא מצאנו תחליף.
hamis'adá she'ahávnu nisgerá bashaná she'avrá ume'áz lo matsánu takhlíf
The restaurant we loved closed last year and we haven't found a replacement since.
4. Reaching for כי as the everyday that. Not wrong — that is the point — but it is register, and a learner who uses it in conversation sounds like a news bulletin. Both sentences below are correct, and they are not saying the same thing about who is speaking.
השר הודיע כי הוא מתפטר בסוף החודש.
hasár hodía ki hu mitpatér besóf hakhódesh
The minister announced that he is resigning at the end of the month. (formal/journalistic)
הוא אמר לי שהוא מתפטר, אבל אני לא מאמין לו.
hu amár li shehú mitpatér, avál aní lo ma'amín lo
He told me he's resigning, but I don't believe him. (m. speaker — what you would actually say)
Key Takeaways
- ש־ is a prefix, written joined, and it does both jobs — complementiser and relativiser — in every register. It is never the wrong answer.
- כי is causal and a complementiser. Milog gives both senses; אמר כי is standard formal Hebrew, not an error.
- But the complementiser כי is a reporting word. Measured on one written corpus: after אמר and ביקש it is an ordinary choice; after רוצה it returns seven hits in the whole encyclopedia, and only five of those are the complementiser at all.
- אשר adds no function ש־ lacks — it is a style choice. The Academy's own punctuation rules illustrate relative clauses with ש־ throughout and use a relative אשר exactly once, inside a quotation.
- באשר ל־ and אשר על כן have no ש־ twin, so they are not style choices at all. כאשר does have one — it is כש־. And מאחר ש־ is not an אשר compound: Milog lists it under אח״ר, "after".
- Two hard errors: never a space after ש־, and never drop it — Hebrew has no bare complement and no bare relative.
- כי cannot introduce a relative clause. המסעדה שאהבנו, never *המסעדה כי אהבנו.
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- ש־, כי or אשר: Which SubordinatorB1 — The three are not three of a kind: ש־ is a bound prefix that does complements and relatives alike, כי is a free word that does complements and causes, and אשר is a free word that does relatives only. Measured on Hebrew Wikipedia, כי and אשר turn out to be in near-complementary distribution — אמר כי in the thousands against three hits for אמר אשר, and 68 for האיש אשר against eight for האיש כי, not one of which is a relative clause.
- כי: BecauseA2 — כי is the everyday word for because — the natural answer to למה and the ordinary way to attach a reason mid-sentence, as in לא עניתי לך כי הטלפון היה על שקט. It is also a second thing that courses leave out: a complementiser meaning that, which is why נמסר כי and הודיע כי are standard news Hebrew rather than mistakes.
- ש־: The Universal SubordinatorA2 — One attached letter does the work English splits across that, which, who and when: אמרתי שאני בא, החבר שהמליץ לי, ביום שהגענו. It is a prefix rather than a word, it is never optional, and it is the building block of אחרי ש־, לפני ש־, כדי ש־, למרות ש־ and the rest of the connective family — most of which have a bare twin that takes a noun instead of a clause.
- אשר: The Formal RelativeC1 — אשר is the free-standing relative marker familiar from legal language, ceremonial prose, the Tanakh and elevated journalism. It normally changes register rather than meaning, while compounds such as כאשר, באשר ל־, אשר על כן and מאשר have developed lives of their own.
- מכיוון ש־, היות ו־, בגלל ש־B2 — Above the everyday כי sits a whole shelf of because-words, and they are not interchangeable: the Academy pairs מפני ש־ and משום ש־ with a reason that follows the main clause, and כיוון ש־ and מאחר ש־ with one that can also come first — a split you can measure. Plus what the Academy really said about בגלל ש (it did not rule), and why היות ו־ is the one to avoid in writing.
- Relative Clauses with ש־A2 — English needs who, which, that — and sometimes nothing at all — to hang a clause on a noun; Hebrew has one invariant prefix for all of it, ש־: השכן שגר מעלינו, הספר שקניתי. This page builds subject and object relatives step by step, shows why ש can never be dropped the way English drops that, and names the roles that need a pronoun left behind instead.