Salmoneus wrote:It's not a spelling pronunciation.
It's also not quite as simple as "thinking there's a /g/ because there's a [g]". Most people do not, for instance, believe there to be /b/ in "debt", or /s/ in "island".
The problem arises in this particular case because people know that there's not just an /n/ in these words - "sing" and "sin" aren't homophones, for instance. But because they have no words (or concepts) to describe the /N/ sound - and because, to be fair, the /N/ sound does sound a bit /g/-ish - they can only describe /N/ as being /n/ plus /g/, as it's spelled (and sort of sounds). So if you tell them there's no /g/, they get confused, because they know there's not just /n/, and they don't have the conscious concept of /N/ as an alternative for what might be there.
After all, if you "drop the G" from "walking", you get "walkin'", with an /n/... it's got an apostrophe and everything! And surely if 'dropping the G' were just turning something from /N/ to /n/ - a change with no loss of elements or gain in simplicity - then it wouldn't be such a common indicator of lazy speech!?
[similarly, some people think there's an /h/ in /S/ and /T/. But this is less common, probably because we don't have any productive, shibbolethical "dropping the H" process].
And even beyond that, because of the history, there are still ways in which [ŋ] behaves synchronically in the phonology of English as if it were a cluster /ng/: it doesn't occur after long vowels/diphthongs, except for in onomatopoeic or expressive words, it alternates with [ŋg] in the comparative and superlative forms of long, strong, young,
and of course, it doesn't occur word-initially or after other consonants. Facts like these make the status of /ŋ/ as a phoneme of English somewhat disputed even among phonetically knowledgeable analysts (apparently, a number of generative phonologists are in favor of analyzing English [ŋ] as synchronically derived from /ng/ (or /n/, before /k/): see this page from The Phonology of Swedish
, Tomas Riad, for some references).
When learning how to do phonetic and phonemic transcriptions, you don't just have to learn about phones, but also about what the traditional/conventional abstractions are for representing specific languages' sound systems. No phonetic transcription is perfectly narrow, and of course a phonemic transcription will only represent one particular analysis of a language—which it is doubtful that everyone will agree on in all respects.