In this paper two different types of vowel reduction are discussed. Acoustic vowel reduction is a loss of vowel quality due to a relaxed articulation in less informative parts of an utterance. The effect of acoustic vowel reduction is illustrated with an experiment. Lexical vowel reduction is the substitution of one vowel by another that is easier to pronounce. It is hypothesized that lexical vowel reduction is the systematic extension of acoustic vowel reduction.