Can you at least define "institution" and "sporadic" for me?
First of all, you don't need to know what 'sporadic' means. You just need to know what sporadic reference is. It's a very technical term.
When we utter a phrase that contains a definite article, such as
the theatre, it can have two very different kinds of reference (situational and sporadic). Another way to say that is that the word
theatre has two very different meanings when it is followed by
the.
1)
the theatre refers to one particular building. This building is material in that it is made of bricks. It takes up space in the town. You can go inside it. When the zombie apocalypse comes, it will still exist, even though nobody will use it. It will still exist even after all humans have died. Eventually the walls will collapse and it will disappear.
2)
the theatre refers to an institution. Institutions are not material. They have no size or shape because they do not exist in the physical world. The society that we live in is structured not by bricks, but by institutions. Banks are institutions, and so are universities, governments, and religions. If there was a zombie apocalypse, almost all of these would cease to exist because they are just ways to understand how our human society is structured. No society, no institutions.
If I'm talking about my personal interests and I say
I love the theatre. I try to go to the theatre once a month, I'm not talking about a particular building. I'm talking about the theatre as an
institution. It's probable that the particular building I go to is different each time, but the institution is the same.
Is that clear now?
By the way, studying that book is really not a good way to improve your grammar.