) and o ( and ) are often not distinguished in pronunciation. ATR harmony Akan vowels engage in a form of vowel harmony with the root of the tongue. -ATR vowels followed by the +ATR non-mid vowels /i̘ a̘ u̘/ become +ATR. This is generally reflected in the orthography: That is, orthographic become i e a o u. However, it is no longer reflected in the case of subject and possessive pronouns, giving them a consistent spelling. This rule takes precedence over the next one. After the -ATR non-high vowels /e a o/, +ATR mid vowels /e̘ o̘/ become -ATR high vowels /i u/. This is not reflected in the orthography, for both sets of vowels are spelled , and in many dialects this rule does not apply, for these vowels have merged. Tones Akan has three phonemic tones, high (/H/), mid (/M/), and low (/L/). Initial syllable may only be high or low. Tone terracing The phonetic pitch of the three tones depends on their environment, often being lowered after other tones, producing a steady decline known as tone terracing. /H/ tones have the same pitch as a preceding /H/ or /M/ tone within the same tonic phrase, whereas /M/ tones have a lower pitch. That is, the sequences /HH/ and /MH/ have a level pitch, whereas the sequences /HM/ and /MM/ have a falling pitch. /H/ is lowered (downstepped) after a /L/. /L/ is the default tone, which emerges in situations such as reduplicated prefixes. It is always at bottom of the speaker's pitch range, except in the sequence /HLH/, in which case it is raised in pitch but the final /H/ is still lowered. Thus /HMH/ and /HLH/ are pronounced with distinct but very similar pitches. After the first "prominent" syllable of a clause, usually the first high tone, there is a downstep. This syllable is usually stressed. Morphology Formation of plural nouns in Akan Akan forms some plural nouns by adding the prefixes 'm' or 'n' to the original word and removing the first sound of the noun. Example include nouns like abofra (child), which forms its plural by removing the 'ab' from the word and adding 'mm' to form its plural: mmofra (children). Same goes for aboa (animal) to mmoa (animals), abusua (family) to mmusua (families), abirekyie (goat) to mmirekyie (goats) etc. in the Twi dialect. The nouns which use the 'n' prefix include; adaka