This paper highlights striking similarities of three well-known but hitherto disparately treated alternations in Germanic morphosyntax: (i) the positional alternation of the finite verb between a low and a left peripheral (V2) position; (ii) the morphological alternation in adnominal adjectives between socalled weak and strong agreement; and (iii) the contrast in definiteness marking between a free DP-initial definite article and a so-called suffixed article. The number and kinds of punctual similarities among these alternations suggest that we are dealing with a parallelism that is non-accidental (even if not always fully surface apparent).In an attempt to propose a principled account of this parallelism, I argue that the familiar syntactic CP/DP analogy must (A) be extended to include the extended adjectival projection (xAP), and (B) that it is more than an analogy. It is, I claim, a point-wise isomorphism. I identify a shared complementizer head C, which, I claim, extended projections of all colors converge on. In Germanic, C is either lexicalized/identified qua head, as d-, or it attracts the lexical category of its containing extended projection, indiscriminately of whether it is verbal, nominal, or adjectival. Movement of the lexical category to the left periphery results, in many cases, in its preceding material which it does not precede in the absence of such movement, notably inflectional material.If correct, the proposed isomorphism hypothesis has consequences for the analysis of the phenomena involved in that it allows us to transfer insights from one domain to another. In particular, it supports an analysis of the adjectival inflection alternation in terms of adjective movement; and an analysis of V2 as involving two merger steps.