What case can be made for considering whether [ə] and [ʌ] are different phonemes or not in American English? Please note the focus is on standard American English. EDIT: i.e.: on General American.

Many dictionaries use /ʌ/ in stressed position and /ə/ in unstressed positions. So we get transcriptions such as:

• DUST /dʌst/
• LOVE /lʌv/
• BACKUP /ˈbækˌʌp/
• KETCHUP /ˈkɛtʃ.əp/
• CUSTOM /ˈkʌs·təm/

However, if these truly constitute two different phonemes, then we should be able to come up with minimal pairs to illustrate the contrast between both sounds.

I cannot think of a single minimal pair to contrast /ə/ and /ʌ/.

It's interesting to look at CMU Dictionary, the pronouncing dictionary of American English.

CMU Dictionary uses AH for both sounds. So we get:

• DUST D AH1 S T
• LOVE L AH1 V
• BACKUP B AE1 K AH2 P
• KETCHUP K EH1 CH AH0 P
• CUSTOM K AH1 S T AH0 M

(0 = unstressed, 1 = primary stress, 2 = secondary stress)

My understanding is that, provided the stressed syllables are pronounced longer and with more energy, saying BACKUP, KETCHUP and CUSTOM as [ˈbækˌəp], [ˈkətʃ.əp] and [ˈkəs·təm] would not hinder comprehension in the least.

As I see it, there's only one phoneme here, which happens to be realized [ʌ] in stressed position and as a schwa [ə] in unstressed positions.

This leaves us with two problems:

• Problem 1 : if /ə/ and /ʌ/ are different phonemes, what are some examples of minimal pairs between the two?

• Problem 2 : if they are allophones, which notation should be used for the phoneme? I assume /ə/.

The reason I'm asking is because I'm teaching American English with a lot of phonemic transcriptions – why teach two phonemes when there's only one.

Finally, where would professional linguists locate those sounds on the following chart (again, from an American point of view)?

The only discussion of the topic I found online so far is on this forum. There's also, to some extent, the Talk section about the ARPAbet article on Wikipedia.

What case can be made for considering whether [ə] and [ʌ] are different phonemes or not in American English? Please note the focus is on standard American English. EDIT: i.e.: on General American.

Many dictionaries use /ʌ/ in stressed position and /ə/ in unstressed positions. So we get transcriptions such as:

• DUST /dʌst/
• LOVE /lʌv/
• BACKUP /ˈbækˌʌp/
• KETCHUP /ˈkɛtʃ.əp/
• CUSTOM /ˈkʌs·təm/

However, if these truly constitute two different phonemes, then we should be able to come up with minimal pairs to illustrate the contrast between both sounds.

I cannot think of a single minimal pair to contrast /ə/ and /ʌ/.

It's interesting to look at CMU Dictionary, the pronouncing dictionary of American English.

CMU Dictionary uses AH for both sounds. So we get:

• DUST D AH1 S T
• LOVE L AH1 V
• BACKUP B AE1 K AH2 P
• KETCHUP K EH1 CH AH0 P
• CUSTOM K AH1 S T AH0 M

(0 = unstressed, 1 = primary stress, 2 = secondary stress)

My understanding is that, provided the stressed syllables are pronounced longer and with more energy, saying BACKUP, KETCHUP and CUSTOM as [ˈbækˌəp], [ˈkətʃ.əp] and [ˈkəs·təm] would not hinder comprehension in the least.

As I see it, there's only one phoneme here, which happens to be realized [ʌ] in stressed position and as a schwa [ə] in unstressed positions.

This leaves us with two problems:

• Problem 1 : if /ə/ and /ʌ/ are different phonemes, what are some examples of minimal pairs between the two?

• Problem 2 : if they are allophones, which notation should be used for the phoneme? I assume /ə/.

The reason I'm asking is because I'm teaching American English with a lot of phonemic transcriptions – why teach two phonemes when there's only one.

Finally, where would professional linguists locate those sounds on the following chart (again, from an American point of view)?

The only discussion of the topic I found online so far is on this forum. There's also, to some extent, the Talk section about the ARPAbet article on Wikipedia.

EDIT (DEC 2018): FYI, I was asking the question in the context of designing an IPA chart for American English (General American), to teach phonetics and ESL, which implies deciding just which phones to teach -- and why.