It is a widely acknowledged truism that mergers in law are nothing of the sort, since the vast majority of deals are essentially takeovers of one practice by a stronger rival.

In this sense, the surprise tie-up between Washington DC giant Wilmer Cutler & Pickering and Boston stalwart Hale and Dorr must be the exception that proves the rule, since rivals concede that the merger – aside from being the biggest in US legal history – is just such a rare beast.