Modern theories of tense define invariant meanings and relate these to variants using a variety of mechanisms. The present theory of tense dispenses with the principle of invariance. The individual meaning variants are derived from original meanings, and in the case of analytical tenses are explained compositionally. After introductory material on the determination of time and on the respective merits of the prototype and the invariance methods, the book contains chapters on aspect in German, on the six traditional tenses and on the structure 'wurde' plus infinitive.