hindi lamang ... kundi pati

The expression hindi lamang ... kundi pati is the formal equivalent of the English 'not only... but also.' In everyday spoken Filipino, the standard equivalent is hindi lang ... kundi pati. The word kundi is a contraction of kung hindi (literally 'if not'), which helps explain why it translates to 'but' in this context. A comma is generally not required before kundi when connecting words or short phrases, but it is used when linking full independent clauses or for stylistic pauses.

1. Structure and Parallelism
For a sentence to be grammatically sound, the elements being linked must be parallel. The phrase is frequently expanded to kundi pati na rin for better flow and emphasis. In this expansion, pati inherently carries the meaning of 'including' or 'also,' while the addition of rin / din provides extra emphasis and redundancy. It functions as a correlative conjunction connecting words or phrases of equal rank. It can be used freely with nouns, adjectives, and verbs. (Note that rin is used after words ending in vowels or semi-vowels w and y, while din is used after words ending in consonants.)

• Nouns: Hindi lamang ang guro, kundi pati na rin ang mga mag-aaral. (Not only the teacher, but also the students.)
• Adjectives: Hindi lamang siya mabilis, kundi pati matalino rin. (He is not only fast, but also smart.)
• Verbs: Hindi lamang siya nagbabasa, kundi pati nagsusulat din. (She is not only reading, but also writing.)

When linking verbs, they must match in Focus and usually Aspect. In the verb example above, both nagbabasa and nagsusulat are in the actor focus and progressive aspect. Additionally, when a preposition like sa is used in the first clause, it generally must be repeated after kundi pati to maintain grammatical balance (e.g., Hindi lamang sa bahay, kundi pati sa paaralan - Not only at home, but also at school).

2. Enclitic Pronoun Placement
Because hindi is a negation word, it attracts enclitic particles and pronouns. The placement depends on the pronoun's length. Monosyllabic pronouns (like ko, mo, ka) must directly follow the first word hindi (e.g., Hindi ko lamang...). Disyllabic pronouns (like ako, siya, kami, kayo) generally follow lamang or lang (e.g., Hindi lamang ako...).

3. The Nuance of 'Pati'
The word pati means 'including' or 'even.' It is actually an optional emphatic addition; the base grammatical pattern is simply hindi lamang ... kundi ... [rin/din]. Using pati here suggests that the second item is a natural extension or an even more noteworthy addition than the first. If pati (or rin/din) is dropped entirely, the sentence translates simply to 'Not only X, but Y', losing the 'also' meaning.

4. Register and Variations
This is a formal pattern. In casual conversation, Filipinos often use lang instead of lamang. A very common way to express 'but also' without using pati is to use the particle rin / din at the end of the second clause (e.g., Hindi lamang siya masipag, kundi mabait din.). In high-formal or literary contexts, the word maging can replace pati (e.g., Hindi lamang sa salita, kundi maging sa gawa).