Demonstrative is the technical term for words like 'this' and 'that'. English has only the two; where 'this' denotes something near or associated with the speaker and 'that' denotes something not so. Most other languages that I've seen (Spanish, Latin, Japanese) separate 'that' into one that denotes something near or associated with the listener, and one that denotes something distant from both of you. So basically a first, second and third person.

Spem has four person-distinctions for this. A first person, a second person, a third person, and a "first and second" person, which denotes something near or associated with both the speaker and the listener.

There's also a time axis. In English (and as far as I can tell the other languages I've seen with three) this/that also has a connotation of "the present or the near future" versus the past. For example, in English:

Spem separates this distinction, so that the vowel in the middle indicates the tense, and the consonant at the end indicates the grammatical person. The consonant at the beginning also can vary to indicate a place instead of a thing.

Present/futurePresent/future, place versionPastPast, place version
First person tem ('this') djem ('here') tɑm ('that') djɑm ('there')
Second person tɵŋ ('that') djɵŋ ('there') tɑŋ ('that') djɑŋ ('there')
First and second tɪr ('this') djɪr ('here') tɑr ('this') djɑr ('here')
Third person tʌn ('that') djʌn ('there') tɑn ('that') djɑn ('there')

Here are some use examples: