Rule 5: Double-breasted suits add breadth, and so should only be worn by slim men.

To reiterate the philosophy behind this series: All rules are there for a reason. They become rules because they have practical advantages.

But there’s nothing wrong with breaking them, as long as you understand those advantages and therefore what you’re losing.

A double-breasted suit adds breadth to a man because it creates horizontal lines. Rather than going straight down, the lapels run across the body.

The buttons, whether there are four or six, create horizontal lines as well. They create a box that naturally adds squareness.

The peak lapels also create breadth because they point outwards – no matter how high on the collar they appear, they add another horizontal line across the top of them.

This is all fairly intuitive. Horizontal lines suggest width – just like belts, checks and cuffs on trousers.

But consider those lines for a minute and think how their breadth-giving properties could be minimised.

(In other words, consider the practical advantages behind the rule – why they are good for a thin man – and play with them.)

The Duke of Windsor, buttoning a DB to the bottom button

A peaked lapel that cuts across the chest as it runs downwards, and ends at a point above a man’s natural waist (so just above his belly button) will create quite a flat line.

But, if it ends lower down, buttoning below the natural waist or even on the hips, the line becomes more vertical.

Now narrow the distance between the waist buttons. The smaller the overlap of the double breast is, the more vertical the line of the lapel will be, and the more its broadening effect is reduced.

That horizontal line of the waist buttons also becomes smaller and less prominent.

A DB with waist buttons closer together

Obviously you don’t want to push this too far, otherwise you might as well have a single-breasted jacket. But slightly adjusting both of these things will make the jacket more slender in a very subtle way.

Lastly, you can reduce the number of buttons on a double-breasted suit. Cutting it to four will make the jacket look boxier. But reducing it to two is a little slimming, as there is only one horizontal line, not two or three.

So there you go. A double-breasted suit does not necessarily make a man too broad. By lengthening the lapel, making it more vertical and reducing the buttons you can create a double-breasted jacket that a large man can wear and will only give him broad shoulders – not a big stomach.