Formal attire: between the morning and the evening

Formal? Morning dress or maybe a stroller.

- B

Nope-- there isn't Afternoon Dress. So your choices are morning or evening.

Except in an ever diminishing range of geography and location, there is almost an exact correspondence in a non-historical discussion of formal and semi-formal wear between being correct and being pedantic.

In the context of a social event where you are asked to dress semi-formally in dinner clothes at 4PM rather than after 6PM, there really is no answer to the question of how one should dress otherwise.

- B

If it 'begins' at 4pm it will probably finish after 6, so black tie would be fine. Unless you feel important enough to change from morning coat to tuxedo at 6pm sharp...

+1 for dinner jacket if the event crosses into evening. For an event that only takes place in the afternoon, I would vote stroller and morning trousers.

Normally I'm not an uber-traditional guy, but the idea (and look of) dinner jackets in sunlight always strikes me as very odd. I wouldn't do it.

Strictly speaking, events starting at 4PM call for morning dress. It's fine to wear it into the evening. It's not fine to wear evening clothes at 4PM by those same standards.

On the other hand, no-one at the event is likely to know they are transgressing unless the OP tells them.

And I would certainly hate being the douchbag wearing a morning suit in a sea of black tie.