International Standards and Conformity Assessment for all electrical, electronic and related technologies
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Verbal forms for expressions of provisions

General

The user of the document needs to be able to identify the requirements he/she is obliged to satisfy in order to claim compliance with a document. The user also needs to be able to distinguish these requirements from other types of provision where there is a choice (i.e., recommendations, permissions, possibilities and capabilities).

 

It is essential to follow rules for the use of verbal forms so that a clear distinction can be made between requirements, recommendations, permissions, possibilities and capabilities.

 

The first column of Tables 3 to 7 shows the preferred verbal form to be used to express each type of provision. The equivalent expressions given in the second column shall be used only in certain cases when the form given in the first column cannot be used for linguistic reasons.

 

Only singular forms are shown in Tables 3 to 7.

 

Requirement

A requirement is defined as follows in the published version of these directives:

expression in the content of a document conveying objectively verifiable criteria to be fulfilled and from which no deviation is permitted if compliance with the document is to be claimed

 

The verbal forms shown in Table 3 shall be used to express requirements.

Table 3 – Requirement

Verbal form

Equivalent phrases or expressions for use in certain cases

shall

is to
is required to
it is required that
has to
only … is permitted
it is necessary
needs to

shall not

is not allowed [permitted] [acceptable] [permissible]
is required to be not
is required that … be not
is not to be
need not
do not

 

EXAMPLE 1
Connectors shall conform to the electrical characteristics specified by IEC 60603-7-1.

 

Imperative mood:

The imperative mood is frequently used in English to express requirements in procedures or test methods.

 

EXAMPLE 2
Switch on the recorder.

 

EXAMPLE 3
Do not activate the mechanism before…

 

 

Do not use "must" as an alternative for "shall". (This will avoid any confusion between the requirements of a document and external constraints – see External constraint).

 

Do not use "may not" instead of "shall not" to express a prohibition.

 

 

Recommendation

A recommendation is defined as follows in the published version of these directives:

expression in the content of a document conveying a suggested possible choice or course of action deemed to be particularly suitable without necessarily mentioning or excluding others

 

The verbal forms shown in Table 4 shall be used to express recommendations.

 

Table 4 – Recommendation

Verbal form

Equivalent phrases or expressions for use in certain cases

should

it is recommended that
ought to

should not

it is not recommended that
ought not to

 

EXAMPLE

Wiring of these connectors should take into account the wire and cable diameter of the cables defined in IEC 61156.

 

In French, do not use "devrait" in this context.

 

Permission

A permission is defined as follows in the published version of these directives:

expression in the content of a document conveying consent or liberty (or opportunity) to do something

 

The verbal forms shown in Table 5 shall be used to express permission.

 

Table 5 – Permission

Verbal form

Equivalent phrases or expressions for use in certain cases

may

is permitted
is allowed
is permissible

need not

it is not required that
no … is required

EXAMPLE 1

IEC 60512-26-100 may be used as an alternative to IEC 60512-27-100 for connecting hardware that has been previously qualified to IEC 60603-7-3:2008.

 

 

EXAMPLE 2
Within an EPB document, if the quantity is not passed to other EPB documents, one or more of the subscripts may be omitted provided that the meaning is clear from the context.

 

Do not use "possible" or "impossible" in this context.
Do not use "can" instead of "may" in this context.
Do not use "might" instead of "may" in this context.
"May" signifies permission expressed by the document, whereas "can" refers to the ability of a user of the document or to a possibility open to him/her.
The French verb "pouvoir" can indicate both permission and possibility. If there is a risk of misunderstanding, the use of other expressions is advisable.

 

Possibility and capability

A possibility is defined as follows in the published version of these directives:

expression in the content of a document conveying expected or conceivable material, physical or causal outcome

 

A capability is defined as follows in the published version of these directives:

expression in the content of a document conveying the ability, fitness, or quality necessary to do or achieve a specified thing

 

The verbal forms shown in Table 6 shall be used to express possibility and capability.

 

Table 6 – Possibility and capability

Verbal form

Equivalent phrases or expressions for use in certain cases

can

be able to
there is a possibility of
it is possible to

cannot

be unable to
there is no possibility of
it is not possible to

EXAMPLE 1
Use of this connector in corrosive atmospheric conditions can lead to failure of the locking mechanism.

 

EXAMPLE 2 
These measurements can be used to compare different sprayer setups on the same sprayer.

 

EXAMPLE 3
Only the reverse calculation approach given in E.3 can be used for calculated energy performance.

 

EXAMPLE 4
The sum over time can be related either to consecutive readings or to readings on different time slots (e.g. peak versus off-peak).

 

Do not use "may" instead of "can" in this context.
"May" signifies permission expressed by the document, whereas "can" refers to the ability of a user of the document or to a possibility open to him/her.
The French verb "pouvoir" can indicate both permission and possibility. If there is a risk of misunderstanding, the use of other expressions is advisable.

 

External constraint

An external constraint is defined as follows in the published version of these directives:

constraint or obligation on the user of the document, typically due to one or more legal requirements or laws of nature, that is not stated as a provision of the standard

 

External constraints are not requirements of the document. They are given for the information of the user.

 

The verbal form shown in Table 7 shall be used to indicate constraints or obligations defined outside of the document.

 

Table 7 – External constraint

Verbal form

Equivalent phrases or expressions for use in certain cases

must

 

EXAMPLE 1       A legal requirement:
European legislation states that opaque eye protection must be worn in these environments.

 

EXAMPLE 2       A law of nature:
diadromous

fish that must obligatorily migrate between freshwater and seawater to complete its life cycle

Do not use "must" as an alternative for "shall". (This will avoid any confusion between the requirements of a document and external constraints – see Requirement).