§ 98 The Corpus of Possession
To constitute possession the animus domini is not in itself sufficient, but must be embodied in a corpus. The claim of the possessor must be effectively realised in the facts; that is to say, it must be actually and continuously exercised. The will is sufficient only when manifested in an appropriate environment of fact, just as the fact is sufficient only when it is the expression and embodiment of the required intent and will. Possession is the effective realisation in fact of the animus sibi habendi.
One of the chief difficulties in the theory of possession is that of determining what amounts to such effective realisation. The true answer seems to be this: that the facts must amount to the actual present exclusion of all alien interference with the thing possessed, together with a reasonably sufficient security for the exclusive use of it in the future. Then, and then only, is the animus or self-assertive will of the possessor satisfied and realised. Then, and only then, is there a continuing de facto exercise of the claim of exclusive use. Whether this state of facts exists depends on two things: (1) on the relation of the possessor to other persons, and (2) on the relation of the possessor to the thing possessed. We shall consider these two elements of the corpus possessionis separately.