In mathematics, indexes are useful to discriminate elements of a set. These elements have common characteristics, symbolized by a same name. The indexes make it possible to differentiate each one of these elements.

Example:

In general semantics, we use indexes with a similar aim. Our goal is to individualize the elements of a set, so as to point out their differences to us, differences that the aristotelian law of identity very often makes us forget. The use of indexes enables us to take into account the first premise ("is not"), at least at the descriptive level (first verbal level).

Examples:

We can thus say "Chair₁ is not chair₂", "Smith₁ is not Smith₂", "Time_Smith is not time_Brown", etc.

Whenever you use indexes, try to find some of the differences between the objects considered.