You might want to clarify what you mean by "professionals"...

In general terms, each type of profession would wear clothing that allowed them to do their job duties in relative comfort and safety (i.e. think of a blacksmith, or butcher, or soldier, or merchant ... all would be considered 'professionals' and would be distinguishable by their garments, but would not have dressed alike).

I would refer you to this reddit post re:the history of the 3-piece suit, as well as this section of the FAQ as it covers the topic far better than I could!