Normal property ownership is something we use to manage scarcity that already exists—that there is only one of something, and we have to decide where it will go and who will be able to decide how it is used. Intellectual property, by contrast, creates artificial scarcity by means of a government-enforced monopoly (in the case of copyright, the monopoly is on the right to produce a copy of a work).
It is unfortunate (and perhaps not accidental) that we settled on the term "intellectual property" as opposed to something more descriptive like "intellectual monopoly." "Intellectual property" encourages equivocating such monopolies with normal property, a mistake that tends to muddle debates on the subject.