The THOG Problem

 

Image: Wikimedia Commons 

You are shown four symbols

1. a black square
2. a white square
3. a black circle
4. a white circle

and told by the experimenter "I have picked one colour (black or white) and one shape (square or circle). A symbol that possesses exactly one of the properties I have picked, is called a THOG. The black circle is a THOG. For each of the other symbols, are they a) definitely a THOG, b) undecidable, or c) definitely not a THOG?" wikipedia (also cf. Futility Closet)