-in-

The -in- completed infix is the standard marker for the completed aspect of most object-focus verbs. It is used with -in, -an, and i- verbs. Note that all ma- verbs (both actor-focus and object-focus) use na- instead, just as mag- and mang- verbs become nag- and nang-. Similarly, actor-focus -um- verbs use -um- for their completed aspect (e.g., kain [eat] → kumain [ate]), not -in-. The -in- infix is also foundational for forming the progressive aspect when combined with syllable reduplication (e.g., basa [read] → binabasa [is reading]).

1. Formation Rules:

• Standard: Insert -in- before the first vowel of the root. Example: basa [read] → binasa [read].
• Suffix Deletion (-in/-hin only): If the verb uses the suffix -in or -hin (e.g., kainin [to eat], basahin [to read]), you drop the suffix. Example: kainin → kinain [ate]; basahin → binasa [read].
• Suffix Retention (-an and i-): Unlike -in verbs, verbs using -an or i- keep their markers. Examples: hugasan [to wash] → hinugasan [washed]; isulat [to write] → isinulat [wrote].
• Colloquial Speech (Dropping 'i-'): In everyday spoken Tagalog, the i- prefix is frequently dropped in the completed aspect. For example, isulat (isinulat) often becomes sinulat [wrote], and ibigay [to give] (ibinigay) becomes binigay [gave].
• Vowel-Initial Roots: If the root starts with a vowel, in- acts as a prefix (e.g., alis [remove] → inalis [removed]). However, i- focus verbs starting with a vowel use ini- (e.g., iabot [to hand over] → iniabot [handed over]).
• The 'ni-' Variant: If the root starts with l, y, r, or w, the infix often becomes the prefix ni- (e.g., luto [cook] → niluto [cooked]). The original infix form (e.g., linuto [cooked], lininis [cleaned]) is still occasionally heard in some dialects or seen in older texts, but the ni- prefix is the modern standard. Occasionally, roots starting with h also allow this as an alternative (e.g., hiram [borrow] → hiniram or nihiram [borrowed]).
• 'i-' Verbs with l, y, r, w Roots: When an i- verb has a root starting with l, y, r, or w, the i- prefix combines with the ni- prefix to form inil-, iniy-, inir-, or iniw- (e.g., ilagay [to put] → inilagay [put]). Colloquially, the i- is often dropped, resulting in just the ni- form (e.g., nilagay [put]).
• With Prefixes: When a verb has a prefix like pag- or pang-, -in- is inserted after the first consonant of the prefix, not the root. Example: pag-aralan [to study] → pinag-aralan [studied].

2. Stress Shift:
When forming the completed aspect of -in verbs, the suffix is dropped and the stress usually returns to the root's original position (e.g., the infinitive basáhin [to read] becomes binása [read]). However, for -an verbs, the suffix is retained and the stress typically remains on the same syllable as the infinitive (e.g., hugásan [to wash] becomes hinugásan [washed]).

3. Aspect vs. Tense:
This form indicates the action is finished, regardless of whether it happened recently or long ago.