Deictic items are those that can only be understood if the listener/reader has additional contextual information. The word itself does not have a definite referent without that information. For example :
A : When are you going to the supermarket again?
B : I shan't be going there again this week. I went yesterday. Do you need something
The items you, I, the, there, this week, and yesterday are all deictic :
- To understand exactly which supermarket is meant by "the" supermarket (exophoric reference), you need access to the shared knowledge of the world of the speaker and listener.
- To fully understand I and you (personal deixis) you need to know who the speaker and listener are - which of course changes between turns. You in the first utterance does not refer to the same person as you in the second utterance
- To understand exactly which days are indicated by this week, and yesterday (temporal deixis) you need to know the date when the utterance was spoken.
- To understand where there refers to (anaphoric reference/spatial deixis) , you need to have heard the preceding utterance in the discourse.