9. Standard language i.e., shall, should, may, and can

Mandatory requirements set within an IEEE standard are clearly distinguished by using specific standard verbs—specifically, shall, should, may, and can.

Shall, should, may, and can are defined in 6.4.7 of the IEEE SA Standards Board Operations Manual.

The word shall indicates mandatory requirements strictly to be followed in order to conform to the standard and from which no deviation is permitted (shall equals is required to).

Note that the word must is deprecated and shall not be used when stating mandatory requirements; must is used only to describe unavoidable situations. The word will is deprecated and shall not be used when stating mandatory requirements; will is only used in statements of fact.

The word should indicates that among several possibilities, one is recommended as particularly suitable without mentioning or excluding others; or that a certain course of action is preferred but not necessarily required (should equals is recommended that).

The word may is used to indicate a course of action permissible within the limits of the standard (may equals is permitted to).

The word can is used for statements of possibility and capability, whether material, physical, or causal (can equals is able to).