A waistcoat is a practical piece of clothing. It keeps the trunk of your body warm, leaves your arms free and pins your tie in place. A waistcoat is also stylish. It allows for the possibility of different colours underneath a jacket and elongates the silhouette.
Unfortunately, a sweater cannot do both.
For similar reasons to those explained above, I would argue that the most practical sweater a man can wear with a jacket is a tank top – sleeveless and with the same shape, essentially, as a waistcoat.
A normal, sleeved sweater underneath a jacket creates needless bulk and heat under the arms. This is particularly true if your suit is of a Scolte-inspired, Anderson & Sheppard-modelled cut, with high armholes. As soon as the temperature rises a little, you immediately feel uncomfortable around the armpits and take the jacket off. The extra layer of clothing down the arms is equally needless and potentially uncomfortable.
So a tank top is practical and, let’s face it, looks fine as long as your jacket stays on. But it is not stylish and is damned to never be so. Occasional trends for geek chic aside, a normal (sleeved) V-neck sweater will always look the most stylish.
This occurred to me a while ago because of a recommendation on A Suitable Wardrobe where Will argued that sleeveless knitwear under a jacket is best as it performs the same function as a waistcoat.
Yes it does. But it’s hard to think of a less stylish knitwear option than the lavender tank top pictured in that post. It may look good under a jacket, but it will be very unflattering once that jacket comes off – which, I admit, most men are more likely to do more often than Will. At the very least a tank top should be just as fitted as a waistcoat, to flatter the physique. Unfortunately, this one is anything but.
I believe supporters of tank tops have unfortunately prioritised practicality over style. This does happen with more traditional gentlemen, as the geekish side of them takes over and they spend their time discussing, for example, the discovery of Russian reindeer leather rather than whether it is being used on an attractive last.
I should also mention that my opinion was backed up by the second in this ASW series – on roundneck sweaters and t-shirts with suits. Generally looks bad, and specifically looks bad in these colours (a pale orange horizontal stripe?)
Sweaters can be practical or stylish under a jacket, but never both.