It's going to have to be trial and error.
The best thing you can do is put small quantities on his highchair for him to try and let him gradually understand the differences.
We didn't have that problem. Both of our kids were DONE with baby food quickly and wanted to eat real food.
Slice some apples or pears, take the skin off and let him gum them if he's willing. I think the problem we make as parents is being scared of letting them learn to chew. We're so afraid they'll have an accident, and we cut things so small, they don't really learn to chew things (by chew, I really mean gum appropriate foods).
At that age, we were giving small quantities of lunch meats (ham/turkey very thinly shaven), real american cheese (from the deli, not individually sliced), well cooked vegetables (frozen mixed vegetables were the favorite with green beans taken out).
The ONLY restrictions in place are those foods that cause choking hazards and those that are a known family food allergen (According to the American Academy of Pediatrics)
When our 4 year-old was transitioning, it was the policy to delay introducing peanut butter, egg whites, strawberries. That is no longer a valid thought. Most experts actually believe that holding off (unless there's a known family allergy) may develop the allergy instead.
Good luck.
Here's a sample menu from AAP's parenting website, HealthyChildren.org:
http://www.healthychildren.org/English/ages-stages/baby/f...