This paper examines the wide spectrum of phonetic properties associated with the phonological distinctions between consonant classes such as /p, t, k/ and /b, d, g/ in a great variety of languages (including languages with multivalued contrasts) and evaluates their relationship to the features [ ± voiced], [ ± aspirated], [ ± fortis]. The discussion separates word-initial, word-medial and word-final positions according to their different production and signalling constraints. A power feature, realized in articulatory timing and/or phonatory power/tension, is set up as the essential differentiator, thus providing a phonetic basis for the fortis/lenis dichotomy. The incorporation of the time dimension into phonology is regarded as a necessary prerequisite to the solution of phonological problems in general and to an adequate treatment of the [ ± voiced] feature in particular, voice onset time being only one temporal asp