DML wrote:I thought business casual was a sport coat.
No. In the business world, where dress policies are often explicitly defined, "business casual" has a very specific connotation for male attire: a shirt with a collar (which rules out t shirts and sweatshirts, but includes dress shirts, polo shirts, etc), long pants that are not blue jeans (most commonly "Dockers" type pants of not-flashy color such as beige, navy, black, etc), and shoes that are not overtly athletic in nature (no sandals, no thongs, no flashy basketball sneakers). It also means NO sportjacket, NO tie. However, Avenues is not "business casual".
I ate at Avenues recently, and it was full. Every gentleman in the dining room (customers and waitstaff alike) wore a sportjacket and a tie, no exceptions. Unless you want to be conspicuous for your attire, I do not recommend dining there without at least a jacket.
There are many, many of our finer dining restaurants, where business casual attire (sans jacket) is the norm, and some where casual attire (e.g. blue jeans, t shirt) is acceptable. There aren't a lot of restaurants in the Chicago area where you would be out of place without at least a jacket - maybe a dozen or so in total - but Avenues is definitely one of them.
Incidentally, one tip I would give to anyone going to Avenues. The staff is really, really eager to please, and they have a lot of flexibility, so don't be reluctant to take advantage of that. For example, if you would like to do the tasting menu but you would prefer a substitution - maybe you don't like something on the tasting menu, or there is something on the a la carte side that appeals to you - or maybe you would like them to not serve the identical items to every member of your party, because you're accustomed to sharing tastes - just ask, and I'm sure they will accommodate.