Most bag advice is about size or colour. The outline matters just as much. A bag is a shape hanging at your hip, and it either repeats the lines in your outfit or breaks them. Neither is wrong, but it helps to know which one you are choosing.

Three outlines, three jobs

A hobo is the soft crescent: a slouchy body that sags a little in the middle, usually carried on one shoulder strap. A bucket is rounded and upright, roughly a cylinder that narrows towards the top, often closed with a drawstring or a flap. A tote is the rectangle: open top, two handles, straight sides.

Think of them as soft, rounded and straight. Each one sits next to your clothes in a different way, and that is the whole idea behind this piece.

Echo or contrast

Look at the dominant line in what you are wearing. Sharp tailoring is made of straight edges and corners. A draped knit with wide trousers is made of soft curves. A big boxy coat is one large block. Then ask what the bag should do:

• Echo repeats the outfit's line. It looks tidy and consistent, and it is the safest choice.
• Contrast adds the opposite line. One curve against straight tailoring, or one hard edge against soft layers, looks deliberate and keeps the outfit from going flat.

Try the pairings below. Pick a bag outline and an outfit and read what the combination does.

Which pairing to choose

There is no single right answer, but a few habits hold up. If you wear a lot of one kind of line, say tailoring, a bag with the other line is the quickest way to add interest. If your outfit is already busy, an echo calms it down. Most people own one soft bag and one structured bag, and that pair covers most outfits.

Look at the outfit's main line first, then decide whether the bag should repeat it or break it.

When to break the rule

Treat echo and contrast as a starting point. A slouchy hobo with a sharp suit is a classic for a reason, and a tote with a knit is the standard commuting outfit. Size and colour can override shape: a very small bag in a strong colour will read first as a colour, whatever its outline. Also consider what you carry. A bag that holds your laptop is a different object from one that holds a phone and keys.

What to look for

• A shape you can describe in one word. Crescent, cylinder or rectangle. If you cannot name it, it will be hard to pair.
• A body that holds its outline. Check whether the bag keeps its shape when empty. A soft hobo should slouch on purpose, not collapse.
• A strap that suits the way you carry it. Shoulder, crossbody or in the hand, and long enough to clear your coat.
• A surface with no loud branding. Plain hardware and a single colour make a bag easy to pair at any price.

Everything above works with a bag you already own. If you want to try a different outline, second-hand is a good place to look.