It is perhaps not clear what the difference between a sweater and a cardigan is. They seem to be the same thing; or at least people use the terms interchangeably. The real answer is whether you’re speaking from a United Kingdom viewpoint or a United States viewpoint.
In the UK, a sweater is something worn over the shirt or blouse and doesn’t have buttons or front closures. But in the US a cardigan with buttons or other closures can be called a sweater.
The cardigan is a comfortable outer garment for the upper part of the body which can add warmth as well as style. The real advantage of the cardigan to a pullover (or sweater) is that it can be worn open like a jacket. This gives a more relaxed look and can be done to cool off if the heavier knit becomes too warm after a while.
With lighter cardigans, it is quite comfortable to wear them in the mornings or evenings even when the weather is warmer and then simply open them up or take them off as the day progresses or when it’s time to retire.
A comfortable, fashionable piece of attire, the cardigan is many times worn about the house or place of work where a/c can be comfortable to some but a bit cool for others. All-in-all, this never-out-of-fashion addition to your wardrobe is an inexpensive savior!