Trousers & Trews

The trouser scene is fairly straightforward in that there are only two types - those with the conventional waistband and those with the high-waisted fishtail back,  suitable for wearing with the Prince Charlie (coatee) and waistcoat. Photo Kinloch Anderson.

Conventional.  These can be worn on all occasions where plain trousers would be worn. As with normal day-to-day trousers, there's a great variety of special features than can be incorporated - pleats at the front, buttons for braces (suspenders in the US), stitched-in creases etc., pockets . . . no pockets,  standard belt loops or the wider loops for a kilt belt. Alternatively they can just have  side tabs for tightening the waistband.
Tartan trousers can be can be worn with a variety of informal and semiformal Highland outfits or just as another pair of trousers.

Left. Trews (from the Gaelic truibhas) differ from trousers in that they're designed for evening wear in place of a kilt. The style is military and the Argyll trews have a
high 3 inch (7.6cm) waistband, with 3 inch wide belt loops for a kilt belt. Trews offer an extremely smart alternative to the kilt and are usually worn with a short jacket such as the Prince Charlie. Photo courtesy Kinloch Anderson.

The normal kilt belt can be worn but if a waistcoat (a vest to our north American friends) is worn, then the belt can be dispensed with.
Trews are often tighter in the leg than trousers but nowadays it does depend upon individual preference. Because they sit higher on the waist than normal trousers, they're usually worn with braces (suspenders) and the back is in a fishtail shape as shown.
Ordinary dress shoes or boots can be worn with trews rather than the conventional brogues.
Trews make a very useful addition to a Highland outfit in that the wearer can ring the changes if attending a series of evening functions - alternating kilt and trews. We wouldn't want to be seen in the same Highland outfit on two consecutive nights now . . . would we?

Not recommended unless you've had a good-taste bypass or are under 20 and in a punk band.