The historical origin of obstruent phonemes in English traces back to the Indo-European system. This paper attempts to account for two important developments (Grimm`s Law and Middle English phonemicization) within the framework of Optimality Theory. The proposal is crucially based on the rejection of a serial interpretation of Grimm`s Law and the substitution of the Maintain Contrast constraint with the interactions between symmetry in the system and the minimality of phonological change. In addition symmetry is claimed to function as a guiding principle whose manifestation can be extended to Middle English phonemicization. It is also shown that the application of nonsystemic faithfulness constraints to the systemic domain enables us to state a formal definition of the types of phonemic change.