On 16 January 2020 at 14.20.03, Ben Coman (btc@openinworld.com) wrote: An error message like "Blah doesn't understand self" is a bit complex for a beginner to decipher. I would like to second this one! If you want to have *beginners mode*, I think you need to include run-time aspects as well as Ben mentions. It should be possible to put the general doesNotUnderstand in a beginners mode, which checks for these cases - messages send to nil, explaining what is the likely cause(s). - the case mentioned by Ben - check if the message is understood by the class or object (several have mentioned the class/object side issue). - check which classes implements the method which was sent, and perhaps even suggest to open the implementers browser Good luck with the project! Best, Kasper