Prefer -a- as the standard determiner for nouns

In English (and this entire discussion applies pretty much to Dutch as well), there are many alternatives for expressing that a rule applies to all cases. Among these alternatives, it is convenient to choose a simple indefinite article (a or an - click Good grammar and style for the difference).

“A client ...” means: “Each time a client comes along who spends …”:

Prefer:	Rather than:
A client who spends over € 50,000 in a given year must be assigned a Personal Coach.	Every client who spends ...
A client who spends over € 50,000 in a given year must be assigned a Personal Coach.	All clients who spend ...
A client who spends over € 50,000 in a given year must be assigned a Personal Coach.	Clients who spend ...
A client who spends over € 50,000 in a given year must be assigned a Personal Coach.	Each client who spends ...
A client who spends over € 50,000 in a given year must be assigned a Personal Coach.	Any client who spends ...

Why?

The alternatives really mean exactly the same thing. But if you stick with a(n)…,

• Your readers do not need to switch between all these alternatives and worry if perhaps the differences mean something.
• A rulebase with many rules is easier to scan through if you go for uniformity.
• As a writer, you do not need to make a choice between alternatives that mean the same thing anyway.

If you have 2 times a, usually one of these must be replaced by the:

Write:	Avoid:
The destination port of a flight booking must be specified.	A destination port of a flight booking must be specified.

If there are no conditions at all, a sounds strange. Prefer each in these cases:

Good:	Less good:
Each Gold Card customer must be assigned a personal coach.	A Gold Card customer must be assigned a personal coach.

With a(n) …, you write in the singular. As a result, you are often confronted with he or she:

Prefer:	Rather than:
An incoming passenger must pass ID control before she is allowed to pass customs.	Incoming passengers must pass ID control before they are allowed to pass customs.

tip

One simple gender-neutral strategy is to switch regularly between he and she, just randomly choosing one or the other. You can also write he or she but this makes a rule harder to read.

… is the fact that … is a set phrase that always contains the, not a:

Write:	Avoid:
A flight booking is the fact that a client books a flight.	A flight booking is a fact that a client books a flight.