Beginning phonetics students are taught that some varieties of American English have two contrasting reduced vowels, transcribed as [e] and [i], illustrated by the unstressed vowels in the minimal pair Rosa's vs. roses (e.g. Ladefoged 2001, 2005). However, little seems to be known about the precise nature or distribution of these vowels. This study explores these questions through acoustic analysis of reduced vowels in the speech of nine American English speakers. The results show that there is a fundamental distinction between the mid central [e] vowel that can occur in unstressed word-final position (e.g. in Rosa), and high reduced vowels that occur in most other unstressed positions, and might be transcribed as [i]. The contrast between pairs like Rosa's and roses derives from this difference because the word-final [e] is preserved when an inflectional suffix is added, so the schwa of Rosa's is similar to the final vowel of Rosa, whereas the unstressed vowel of roses is the high [i] reduced vowel quality found elsewhere. So the standard transcription of the reduced vowel contrast is justified, but the widespread use of [e] to transcribe word-internal reduced vowels is misleading – mid reduced vowels are generally only found in stem-final position.