Vowel Diacritics in Bengali
It is worthwhile to note that the Bengali script is an 'Abugida', not an 'Alphabet'. An abugida differs from an alphabet by the fact that in an abugida, any vowel following a consonant is written as an diacritic appended with the preceding consonant. This diacritical form is called 'কার' (kar, /kar/) form of the following vowel in Bengali. For example, the 'কার' form of আ is called 'আ-কার' (a-kar, /a kar/). In an abugida, when a consonant stands alone, it is pronounced with an inherent vowel. In case of Bengali, this inherent vowel is 'অ' (ô, /ɔ/). When a vowel diacritical mark is added, it is understood that the inherent অ is removed. If one wants to write only the consonant without the inherent vowel, one adds the 'hasanta' mark (্) with the consonant. The following table shows how the consonant ক is written when followed by the vowels. All other consonant-vowel combinations are formed in the same way.
|Consonant||Following Vowel||Diacritical form of the vowel||Bengali script||Pronunciation|
|ক||No following vowel||None||ক্ (= ক + ্)||/k/|
|ক||আ||া||কা (= ক + া)||/ka/|
|ক||ই||ি||কি (= ক + ি)||/ki/|
|ক||ঈ||ী||কী (= ক + ী)||/ki/ or /ki:/|
|ক||উ||ু||কু (= ক + ু)||/ku/|
|ক||ঊ||ূ||কূ (= ক + ূ)||/ku/ or /ku:/|
|ক||এ||ে||কে (= ক + ে)||/ke/|
|ক||ঐ||ৈ||কৈ (= ক + ৈ)||/koi/|
|ক||ও||ো||কো (= ক + ো)||/ko/|
|ক||ঔ||ৌ||কৌ (= ক + ৌ)||/kou/|
|ক||ঋ||ৃ||কৃ (= ক + ৃ)||/kri/|
|ক||অ্যা||্যা||ক্যা (= ক + ্য + া)||/kæ/|
Take a word in Bengali, say 'mama'. It means 'maternal uncle' in Bengali. For writing it in Bengali alphabet, first break it into syllables : ma-ma. Then take the first syllable, 'ma' and note that its consonant is 'm'. Bengali for 'm' is 'ম'. Now notice that the 'm' is followed by a 'a', that is, a 'আ'. Since the consonant 'm' is followed by the vowel 'আ', we will attach the diacritical or 'কার' form of the vowel 'আ' with the preceding consonant 'ম'. The diacritical form of 'আ' is 'া', from the previous table. So 'ma' in Bengali script is 'মা'. Repeating exactly the same procedure for the remaining syllable, we will arrive at the result, which is 'মামা'.
Vowels - The Vowels section in Bengali Alphabet page in Wikipedia.
Abugida Writing System - The Wikipedia page on Abugida Writing System. This page describes how Abugida writing systems work.
Diacritics - The Wikipedia page on Diacritics. Suggested for further reading about diacritics and how they are used.