This question was answered on our Q & A Wednesday show on June 28, 2017.
The degree to which guests dress up on formal nights falls into a broad spectrum. For some guests, wearing pants (instead of shorts) is dressing up and then you also find those who will wear a tuxedo any chance they get. The mainstream cruise lines, have become more casual over the last several years and other than shorts, t-shirts and swimwear, do not really enforce what guests are wearing. They do still have guidelines which generally means dress slacks or kakis and button-down shirts with optional sport jackets for gentlemen and cocktail dresses for women. If you are planning to visit one of the specialty restaurants onboard your cruise, they typically have more formal dress requirements every evening.