A Question About Allophones

I posted this on the class discussion board today:

Hi Natalie, I’m having a little trouble with the aural manifestations of some allophones given as examples in the book. In particular, the distinction between the [gj] versus the [gw] allophones of [g]. The [gj] sound in the word “geese” is supposed to be different from the [gw] sound of the word “good”. To me, these sound like the same [g] sound, only modified by the vowel that comes after it. I realize that when I physically form my mouth and tongue to make these sounds that they form differently, but I can’t see why they can be classified as different sounds completely. Maybe it’s only because I don’t speak a language that makes this distinction. I guess this is where it would be helpful to discuss these things in person rather than online. thanks