Tone sandhi is when the pitch pattern (tone) of a syllable changes when it is followed by another syllable in continuous speech.
The MTL (Modern Taiwanese Language) writing system is designed to simplify tone sandhi. It's sandhi-aware, meaning the way a multi-syllable word is written already shows the changed tone of the preceding syllables.
In continuous speech, the basic rule is that all syllables in a word change tone, **except** under specific conditions:
Example: In the sentence "Lie karm u pid? U, goar u cidky," the words *pid*, *cidky*, and *U* keep their original tones because they mark the end of a phrase or sentence. The other words (*Lie*, *karm*, *goar*) change tones.
Nouns and gerunds (verb forms used as nouns) generally DO NOT change tone.
The Big Exception: Nouns DO change tone when they are used **as adjectives** or **as measure words** (denoting a unit).
Example: In *Taioaan-laang* (Taiwanese person), the noun *Taioaan* (Taiwan) is acting as an adjective and **changes tone**.
Pronouns (like *goar* "I", *lie* "you") DO change tone by default.
Exception: A pronoun DOES NOT change tone if the speaker pauses to **emphasize** it.
When adding the suffix 'ar' (like a diminutive), the front syllable usually changes tone (e.g., *"niaw" → "niau'ar"*).
Exception: If the front syllable has a **flat tone** (Tone 7), it **does not change tone** (e.g., *"te" → "te'ar"*).
MTL offers significant benefits for computational tools like TTS:
The most difficult technical challenge for a Taiwanese TTS system is accurately implementing the Noun/Adjective Exception (where the tone change depends on the word's function).
The Problem: The tone change of a word like *Taioaan* depends entirely on its function in the sentence: Noun (no change) vs. Adjective (change).
The Solution: The TTS system needs a robust Part-of-Speech (POS) Tagger to label every word in the input text as a Noun, Adjective, Verb, etc., before applying the tone rules.
The lack of established, high-quality Taiwanese POS tagging models and large, tagged datasets is currently the main bottleneck for building truly accurate Taiwanese TTS.