It always amazes me how little people use trousers in semi-casual attire.
Contrasting clothing can be beautiful. It's not just about contrasts in texture but about formality, colour and fabric refinement.
A pair of fine wool suit trousers are a perfect base for a semi-casual ensemble with an open-necked shirt, ribbed wool cardigan and black Oxfords; a good combination for a home-hosted dinner party where the suit jacket would be too formal.
Trousers - Marks & Spencer
Cardigan - Zara
Shirt - Hawes & Curtis
Shoes - Zara