This study pertains to a parallelism between the sentence (CP) and the noun phrase (DP) observed in the history of English. We begin by reviewing that doubly-filled COMP constructions were legitimate in Middle English (ME) and Early Modern English (EModE), though they are excluded by the familiar doubly-filled COMP filter in the Present-day English (PDE). Actually, it will be demonstrated, a historical change comparable to that is attested in the noun phrase as well. We propose that this similarity can be captured by postulating a doubly-filled DP filter, a DP counterpart of doubly-filled COMP filter. A theoretical basis for this pair of filters is established by assuming that AGR was present in phonetically overt C and D at the early stages of English, whereas it is absent in both of their PDE counterparts; if Spec-head agreement is triggered by AGR, it fails in the latter case, which amounts to what is banned by the proposed filters.

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