| Can | We use ‘can’ in statements of possibility and capability, whether material, physical, or causal; ‘can’ equates to ‘is able to’ |
| May | We use ‘may’ to indicate ‘is permitted to’; it does not represent uncertainty in a requirement (typically indicated through use of ‘TBD’) |
| Shall | We use ‘shall’; exclusively to indicate an instrument functional or performance requirement |
| Should | We use ‘should’ to indicate an instrument goal |
| Will | We use ‘will’ to indicate a statement of fact |