But you said that the k in "kid" and "cod" sound different because of the following vowel, and I had concluded that myself also. But "kalb" and "qalb" have the same vowel. If you want to pronounce each of them with their "k" to sound like their respective phonemes in "kid" and "cod", you have to force yourself.
Well, in English the quality of the vowel modifies the consonant. In Arabic it's the other way round --- "qalb"
does come out sounding a bit like "qolb". But there won't always be an audible difference between vowels and consonants related to whether they're preceded by k or q.
Further, consider what happens when a root is conjugated or declined. If I remember rightly, the plural of "kalb" is "aklab" and the plural of "qalb" is "quluub". So one can't think that it's the quality of the following sound that determines whether the consonant is a "k" or a "q" --- it's always the quality of the
consonant which remains constant when such grammatical changes take place.
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The usual rule for transliterating Arabic is to do it letter for letter from their alphabet. So for example we would write "al shams" ("the sun") when it is pronounced "ash shams" --- because the Arabs always write the consonant in "al" as an "l" however it's pronounced. This is arguably a bad way to transliterate Arabic, but it's the method almost universally followed.
Now in the case of "k" and "q", they have two different letters, which we therefore transliterate differently, whereas, if they mark vowels at all (which is not usually done in Arabic, but which is an optional extra) they would use the same vowel marking for the vowel in "kalb" as for the vowel in "qalb".
Edited by Dr Adequate, : No reason given.