In An Introduction to Roman Law, Nicholas explains that the question of whether a person can be considered to be in possession of a thing is both a question of fact and a question of law:

The notion that “possession” is somehow both a matter of fact and a matter law is often repeated in respect of the common law as well. It can be seen in the common practice of qualifying the word by using terms such as “legal possession”, “constructive possession”, “deemed possession” and “possession in the eyes of the law”. Writing in this vein, for instance, Clarke and Kohler state, “A person who takes physical control of land or goods, with the intention of excluding all others from it or them, acquires possession of it or them as a matter of law”. It can also be seen in the other common practice of distinguishing between using the word to denote a fact and using it to describe a legal concept. Pollock and Wright adopt this approach, drawing a distinction between using “possession” to denote “an actual relation between a person and a thing”, and using it to describe “the state of being possessor in the eyes of the law”. Whilst “possession” may describe a factual state of affairs, these various approaches to possession each suggest that its meaning, at least in part, is defined by law. This chapter aims to explore and ultimately defend this characterisation of possession.

In the first section we will see that lawyers normally use the word “possession” to denote a factual state of affairs. The proof of this is that any litigant wishing to rely on a legal rule which makes reference to “possession” will usually have to introduce evidence of possession.