ter- / di-

In Indonesian, the passive voice is not just about changing the focus of the sentence; it also conveys the nature of how the action occurred.

1. The Default Passive (di-)
The di- passive is the standard, neutral form. While it often describes intentional acts, it is the default choice for reporting events. With a simple first- or second-person actor, the object-voice model is normally preferred in edited Indonesian, as in Buku itu saya baca. This is not an exceptionless ban on di- with those persons: TBBI gives Tugas itu harus diselesaikan oleh kamu dan saya with coordinated pronouns. In a third-person passive, the agent is optional, and if the agent follows the verb immediately, the word oleh (by) is often optional (e.g., Buku itu dibaca (oleh) Budi).

2. The Uncontrolled Passive (ter-)
The ter- prefix is used specifically when you want to emphasize that an action was not deliberate or to focus on a specific result. It has three distinct nuances:

• Accidental: The action happened without intent. (e.g., terinjak - accidentally stepped on).
• Stative/Resultative: Focuses on the state. (e.g., terbuka - is in an open state). A state reading need not mention an actor. An actor phrase and the lexical verb help determine the reading; adding an actor does not by itself prove an accident.
• Potential: Indicates that something can be done, often used with tidak to mean 'cannot be done' (e.g., Tulisan itu tidak terbaca oleh saya - That handwriting cannot be read by me).

3. Key Differences in Usage

• The Role of 'Oleh': An explicit actor in an accidental ter- construction can be introduced by oleh. An explicit oleh phrase is a clear model with a pronoun, as in Buku itu terbawa oleh saya. TBBI also gives ter- examples with an immediately following noun actor and no oleh. Do not infer an exceptionless pronoun-versus-noun requirement from these examples alone.
• Agent Flexibility: Accidental ter- constructions can name first-, second- or third-person actors. Crucially, ter- passives do not change structure based on the person of the actor. In the model shown here, the actor phrase follows the verb, and ter- verbs cannot be used in the object voice structure (e.g., Buku itu saya terbawa is incorrect; it must be Buku itu terbawa oleh saya).

4. Morphological Rules for ter-
Unlike di-, which never changes, ter- can change based on the root word:

• If the root starts with 'r', it becomes te- (e.g., terasa).
• If the first syllable contains 'er', it often becomes te- (e.g., tepercaya).
• A few irregular roots take tel- (e.g., telanjur, telantar).

5. The Colloquial Equivalent (ke-)
In everyday spoken Indonesian, the formal ter- prefix is heavily replaced by the colloquial ke- prefix for accidental and potential actions. For example, terbawa becomes kebawa (accidentally taken), and terinjak becomes keinjak (accidentally stepped on).

Valid Variants and Intended Focus: Buku itu terpilih oleh Budi kemarin can focus on the outcome of selection; it need not claim accidental choice. Buku itu dipilih oleh Budi kemarin neutrally reports the event. Likewise, Laporan itu saya tulis is the ordinary object-voice model with saya; di- and an explicit actor belong to a different construction, not an intrinsically impossible person combination.