Agents with โดย and Omitted Agents | Thai Grammar

English normally expresses a passive agent after the event with by. Thai has two important possibilities: a short agent can occur directly between ถูก/โดน and the action, while โดย + agent can follow the action in formal writing, either after a passive marker or in a markerless patient-first clause. Thai also omits the agent freely when it is unknown, generic, obvious, deliberately backgrounded, or simply not relevant.

This is not optional decoration on one fixed passive template. Agent placement interacts with the passive strategy, register, and information structure. เด็กถูกสุนัขกัด is a compact ordinary affected-subject passive; รายงานถูกจัดทำโดยฝ่ายวิจัย is formal institutional packaging; กระจกถูกทุบแตก leaves the actor unspoken. See when Thai avoids a passive for the wider discourse choice.

Three core agent choices

Choice	Productive frame	Best fit
integrated bare agent	patient + ถูก/โดน + agent + predicate	short agent; affected event
postverbal โดย agent	patient + (passive marker +) predicate + โดย + agent	formal, bureaucratic, news, academic; marker may be absent
agent omitted	patient + passive marker + predicate	unknown, obvious, generic, or backgrounded actor
source after ได้รับ	recipient + ได้รับ + noun/result + จาก + source	receipt, support, effect, institutional source
active alternative	agent + predicate + patient	agent is important or natural discourse topic

เด็กถูกสุนัขข้างบ้านกัดที่ขาครับ

dek thuk sunak khang ban kat thi kha khrap

The child was bitten on the leg by the neighbor's dog. (ordinary polite report, male speaker; integrated agent)

ผู้โดยสารถูกเจ้าหน้าที่ขอให้เปิดกระเป๋าค่ะ

phu doisan thuk chaonathi kho hai poet krapao kha

The passenger was asked by an official to open her bag. (formal-neutral report, female speaker; official is agent of the request)

รายงานฉบับนี้จัดทำโดยฝ่ายวิจัยครับ

raingan chabap ni chat tham doi fai wichai khrap

This report was prepared by the research department. (formal report, male speaker; markerless patient-first clause with a postverbal โดย agent)

The integrated agent precedes the main action: สุนัข...กัด, เจ้าหน้าที่...ขอ. Formal โดยฝ่ายวิจัย instead follows the action and makes the actor relation explicit even though this example has no ถูก. English-speaking learners often mix these orders by putting a bare agent after the verb; Thai needs either the integrated position or an explicit formal relator.

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For a short ordinary agent, start with patient + ถูก/โดน + agent + verb. Reserve postverbal โดย + agent mainly for formal prose and institutional statements; in that register, it can also follow a markerless patient-first predicate.

Why an agent is often absent

A passive construction backgrounds the actor by design. If the speaker does not know who acted, if any member of an institution could have acted, or if the result matters more, omitting the agent is the natural choice.

จักรยานคันใหม่ของฉันถูกขโมยเมื่อคืนค่ะ

chakkayan khan mai khong chan thuk khamoi muea khuen kha

My new bicycle was stolen last night. (ordinary polite report, female speaker; unknown agent omitted)

ถนนช่วงหน้าตลาดกำลังถูกซ่อมอยู่ครับ

thanon chuang na talat kamlang thuk som yu khrap

The section of road in front of the market is being repaired. (formal-neutral update, male speaker; institutional agent irrelevant)

คำสั่งซื้อเลขนี้ถูกยกเลิกแล้วค่ะ

kham sang sue lek ni thuk yokloek laeo kha

The order with this number has been canceled. (formal-neutral service update, female speaker; outcome foregrounded)

Agent omission does not turn the event into an intransitive predicate. Theft still implies a thief and repair still implies repairers, but Thai leaves them outside the asserted information. This differs from a true resultant state such as ประตูเปิดอยู่, which need not assert an opening event at all.

Omission can also be a tactful discourse choice when naming responsibility would be confrontational. That pragmatic effect comes from backgrounding, not from a special polite-passive form.

โดย marks an actor, not every English by-phrase

Formal โดย can identify the performer or institutional author of an event. It is not a universal translation of English by. Means and instruments commonly use ด้วย; causes often use เพราะ; routes and deadlines require other relators.

ระบบใหม่นี้ได้รับการพัฒนาโดยทีมวิศวกรไทยค่ะ

rabop mai ni dai rap kan phatthana doi thim wisawakon thai kha

This new system was developed by a Thai engineering team. (formal report, female speaker; institutional agent with โดย)

กล่องถูกตัดด้วยมีดคัตเตอร์ครับ

klong thuk tat duai mit khattoe khrap

The box was cut with a utility knife. (ordinary polite report, male speaker; instrument with ด้วย, not agent โดย)

เที่ยวบินล่าช้าเพราะฝนตกหนักค่ะ

thiao bin la cha phro fon tok nak kha

The flight was delayed because of heavy rain. (formal-neutral report, female speaker; cause with เพราะ, no passive agent)

An inanimate cause can occupy the integrated position when it genuinely participates in the event: ประตูถูกลมพัดปิด “the door was blown shut by the wind.” But โดยฝนตกหนัก would not replace causal เพราะฝนตกหนัก.

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Classify the relation before choosing a relator: โดย identifies a formal event agent, ด้วย marks an instrument, จาก often marks a source, and เพราะ introduces a cause.

Agents inside longer predicate chains

The noun after ถูก/โดน is the agent of the following predicate, but later predicates may introduce new participant relations. In a directive chain, the affected subject can become the actor of the embedded event.

พนักงานถูกผู้จัดการสั่งให้แก้ใบเสนอราคาใหม่ครับ

phanak ngan thuk phu chatkan sang hai kae bai sanoe rakha mai khrap

The employee was ordered by the manager to revise the quotation. (formal-neutral workplace report, male speaker; employee becomes actor of แก้)

Here ผู้จัดการ performs สั่ง, while พนักงาน is both the affected subject of the order and the understood actor of แก้. ให้ opens the ordered event. The entire chain cannot be decoded by matching each word to English by or to.

In a beneficial receipt frame, the source follows later:

ผู้ป่วยได้รับความช่วยเหลือจากทีมกู้ภัยอย่างรวดเร็วค่ะ

phu puai dai rap khwam chuai luea chak thim ku phai yang ruat reo kha

The patient quickly received help from the rescue team. (formal-neutral report, female speaker; source of assistance with จาก)

The rescue team is semantically responsible for the help, but จาก fits the received-benefit construction more naturally than inserting it as a bare agent after ได้รับ.

Time, aspect, and negation

Agent expression does not determine time. เมื่อวาน anchors past reference, กำลัง...อยู่ marks an ongoing event, จะ gives prospective viewpoint, and แล้ว marks current relevance. The main predicate remains invariant.

เอกสารยังไม่ได้ถูกลงนามโดยผู้อำนวยการค่ะ

ekkasan yang mai dai thuk long nam doi phu amnuai kan kha

The documents have not yet been signed by the director. (formal administrative update, female speaker; negative passive and formal agent)

โรงพยาบาลจะประกาศผลการตรวจพรุ่งนี้ครับ

rongphayaban cha prakat phon kan truat phrung ni khrap

The hospital will announce the test results tomorrow. (formal-neutral report, male speaker; natural active packaging when the institution matters)

Even in administrative contexts, active order is often clearer when the responsible institution matters. A โดย phrase is useful when the affected participant or outcome is already the topic, but it is not a requirement of formal prose.

Ordinary-polite dialogue

Two colleagues review a revised contract.

สัญญาฉบับนี้ได้รับการแก้ไขโดยฝ่ายกฎหมายหรือคะ

sanya chabap ni dai rap kan kaekhai doi fai kotmai rue kha

Was this contract revised by Legal? (polite question, female speaker; formal agent phrase)

ใช่ครับ ฝ่ายกฎหมายแก้ไขเงื่อนไขข้อสุดท้าย

chai khrap fai kotmai kaekhai ngueankhai kho sutthai

Yes. Legal revised the final condition. (ordinary polite reply, male speaker; active order because agent is now topical)

แล้วได้รับการตรวจจากผู้บริหารหรือยังคะ

laeo dai rap kan truat chak phu borihan rue yang kha

And has it been reviewed by management yet? (polite question, female speaker; contract omitted as recoverable)

ตรวจแล้วครับ แต่ยังไม่ได้ลงนาม

truat laeo khrap tae yang mai dai long nam

It has been reviewed, but it hasn't been signed yet. (ordinary polite reply, male speaker; agents omitted as irrelevant)

Common Mistakes

1. Putting a bare agent after the passive verb

❌ นักเรียนถูกเรียกครูค่ะ

Incorrect for ‘the student was called by the teacher’; the bare agent is in the wrong position.

✅ นักเรียนถูกครูเรียกไปพบหลังเลิกเรียนค่ะ

nakrian thuk khru riak pai phop lang loek rian kha

The student was called in by the teacher after school. (ordinary polite report, female speaker)

2. Putting โดย before the action

❌ รายงานถูกโดยผู้เชี่ยวชาญตรวจสอบครับ

Incorrect—postverbal โดย follows the event it attributes.

✅ รายงานถูกตรวจสอบโดยผู้เชี่ยวชาญด้านความปลอดภัยครับ

raingan thuk truat sop doi phu chiao chan dan khwam plotphai khrap

The report was reviewed by a safety expert. (formal report, male speaker)

3. Marking an instrument as an agent

❌ เชือกเส้นนี้ถูกตัดโดยกรรไกรค่ะ

Wrong for ordinary instrument meaning; scissors are the tool, not the institutional or intentional agent.

✅ เชือกเส้นนี้ถูกตัดด้วยกรรไกรเล็กค่ะ

chueak sen ni thuk tat duai kankrai lek kha

This rope was cut with small scissors. (ordinary polite report, female speaker)

4. Forcing an agent into a result-focused update

❌ คำสั่งซื้อถูกยกเลิกโดยใครไม่ทราบแล้วครับ

Awkward packaging—the unknown-agent phrase interrupts a simple result update.

✅ คำสั่งซื้อรายการนี้ถูกยกเลิกแล้วครับ แต่ยังไม่ทราบว่าใครเป็นผู้ยกเลิก

kham sang sue raikan ni thuk yokloek laeo khrap tae yang mai sap wa khrai pen phu yokloek

This order has been canceled, but it is not yet known who canceled it. (formal-neutral update, male speaker)

5. Treating every English by as โดย

❌ รถติดโดยมีอุบัติเหตุข้างหน้าค่ะ

Incorrect causal relation—โดย does not replace English ‘because of.’

✅ รถติดเพราะมีอุบัติเหตุข้างหน้าค่ะ

rot tit phro mi ubattihet khang na kha

Traffic is backed up because there is an accident ahead. (ordinary polite information, female speaker)

Key Takeaways

A short agent normally appears between ถูก/โดน and the main predicate.
Postverbal โดย + agent is especially formal and can occur with or without an overt passive marker; active order is often clearer in conversation.
Omit agents that are unknown, obvious, generic, tactfully backgrounded, or irrelevant.
Distinguish agent โดย, instrument ด้วย, source จาก, and cause เพราะ.
In longer chains, track each role separately; the passive agent need not be the actor of every later predicate.

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