Are you saying 4 o’clock or 16 o’clock?

Answer

There is no linguistic veto against “4 o’clock” when you mean “4 o’clock”, simply because this issue has nothing to do with the language or the language system itself (unlike grammatical issues, for example). Rather, it is about conventions specific to certain cultures.

In the western world, as you point out, there are two systems for displaying the time: one of 12 hours and one of 24 hours. In Anglo-Saxon culture, only the former is widespread, with am and pm. – for times before noon and after noon respectively – are added if the part of the day is important to be able to interpret the message. The second does exist, but is only used in a very limited number of contexts where precision is important, such as in military operations.

What is the current practice in Dutch? We use the 12-hour system in situations where the context usually makes it sufficiently clear which part of the day we mean and where we can quickly detect and remedy any confusion (especially in spoken language), e.g. by adding in the afternoon. The 24-hour period is reserved for situations where context is more difficult to deduce, confusion is not immediately detectable and precision is important (especially in written language).

For example, you will never hear newsreaders or radio and television presenters use the extensive system, but you will, for example: The 7 o’clock news with Freek Braeckman (it is clear to everyone that it is evening), or At 4 o’clock in the morning the C-130 landed op Melsbroek (tonight makes the sentence unambiguously interpretable). On the other hand, letters, invitations, conference programs, etc. always mention the time according to the elaborate system. Another example: announcers use the short system to announce when a program is scheduled (e.g. Bruno Wyndaele will be there at eight o’clock with “The bounty hunters”), while the program overview in newspapers and magazines shows the same program with the extended system. announces (e.g. 20.00 The Bounty Hunters).