Ownership is not likely to stand out in most people’s minds as either the most central or the most illuminating case of an office. And, yet, I will argue in this article that the idea of ownership as an office is especially revealing of a tension between the concept of an office and the normative significance of offices in a legal order, a tension that property law resolves in a particularly revealing way with respect to ownership. The tension between the concept of office and its normative significance amounts to this: whereas offices are always capable of vacancy because they are impersonal positions of authority separable from the office-holder, the law abhors vacancies in principle. In earlier articles, I have explained how horror vacui motivates property law’s concern ‘to see that the office of ownership is filled.’ In this article, I will explain how and why vacancy in office amounts to a defect in the legal order itself – in brief, because vacancy undermines the effectiveness and, ultimately, the legitimacy of law as a system for allocating authority. I will argue that the potential for vacancy in offices combined with law’s horror vacui leads to possession as a default procedure for appointment to offices, in general, and the office of ownership, in particular.