Actually, in the expression you are discussing, most dialects of English (that includes American English) do NOT replace the /t/ sound with a /d/, though I can understand why you may think it sounds like that.

What happens is this:

1) In certain contexts “voiceless stops” –/t/, /k/ and /p/– are “aspirated”, that is, they are followed by an explosive puff of air. When this happens it is very easy for us to HEAR that it is the voiceless version of the sound that is being used, and NOT its voiced relative (d, g and b, respectively). When they are NOT aspirated, they sound much more like the voiced versions, though if you compare them very closely, you will discover that they usually are NOT voiced.

2) In many dialects, including American ones, especially what we might call “Standard American” (SA), this aspiration is much more limited than in others, like “Received Pronunciation” (RP) in England. Common situations where BOTH SA and RP aspirate these sounds are at the beginning of a word (tea, come, key, pay) and at the very end after a vowel (got, sack, rip).

(If you place you hand an inch from your mouth while pronouncing these words you will feel that puff of air. You can actually, with some effort, say this words WITHOUT aspirating these sounds, but it can be difficult and sound a bit odd!)

Compare, for example, the pronunciation of “British”. RP aspirates it, SA does not. But, despite what some think, and what a FEW may actually do, the SA version is NOT “Briddish”.

Perhaps you’ll see (hear!) what I mean if you try to say “Godda” with a deliberate and clear use of the VOICE for the /d/ sound. It may sound akin to “Gotta” but NOT the same.

3) BUT you are correct to note the difference between the /t/ in “got” and in “got a. . . “. It’s just that the difference of aspirated and unaspirated /t/. As noted in #2 above–a FINAL /t/ after a vowel aspirates the /t/. But in real speech we do not pronounce every word in isolation. We often combine them. So, in this case, “got a” is pronounced much the same as a two-syllable word with the accent on the first syllable. In this context, between two vowels, SA does NOT aspirate the /t/. (On the other hand, when I say something like “I got five letters”, where the /t/ is followed by another consonant, I end up aspirating it.)

So, no, it’s not a /d/ at all…. and it is NOT based on “laziness”. (As for the use/non-use of aspiration, that is simply a dialectal variation, that goes back long before RP was established.)

/t/ and /d/ are called “dental” sounds in linguistics. Because they are similarly pronounced (by placing the tongue against the teeth) they can often be changed in speech. Because the sounds are very similar in the way they are made in the mouth, the meaning is understood.

The Latin language also used D’s and T’s in several of their inflected words. (amare, to love, amantis, of those loving, amandum, the loving ones). We see this today in such words as comment and commend. This interchangeability could logically flow to other words that end in T or D.

It is a natural effect of how languages work.

well my theory, or at least my conceptualization is that when you pronounce the t on the end of a word, unless you pointedly make it sound like a T. you are essentially pronouncing it “on the end of the word”.. and it just doesn’t get pronounced well enough to sound like a T. the British, for example. have a couple ways of dealing with this. they say for “it is” which we say (id is) they say “i tis”. if you put the t sound, onto the next vowel, it remains a T. if you pronounce it on the end of the word, it turns into a D. but of course there also is the glottal stop, were the T at the end of a syllable/word is just ignored completely.

It’s essentially down to laziness. Think about how you form the sounds ‘t’ and ‘d’ (not the names of the letters, but their sounds in either ‘got a …’ or ‘godda…’).

They both involve having the tip of the tongue touching the roof of the mouth just behind the front teeth, but the ‘t’ sound require a little more control of the tongue. So when speaking quickly and imprecisely, the ‘d’ sound takes less time and effort.

Just think about it. Say the /t/ sound over and over again. It gradually transforms into the /d/ sound. Laziness explains much of the English language, especially casual English or regional accents.

The Romans used “id” instead of “it,” because they knew that’s what it sounded like (id = it) heh heh heh.

if you speak correctly it dosent and that’s from a brummie!