Types in Common Lisp may or may not be represented by classes (all classes are types, not all types are classes). In this case, character is indeed a class, whi

Types in Common Lisp may or may not be represented by classes (all classes are types, not all types are classes). In this case, character is indeed a class, while base-char is not. It's definitely true to say that base-char is a subtype of character, in that some characters are also base-chars, while others are not. (The spec defines that there are at least 96 standard characters, all of which are of type standard-char, and thus also of type base-char. Implementations may add others. Interestingly, the spec doesn't define how those characters are encoded; of course most modern implementations use some variant of Unicode.) Some examples: (typep #\A 'base-char) ⇒ true (typep #\A 'standard-char) ⇒ true (typep #\A 'extended-char) ⇒ false (typep #\A 'character) ⇒ true (typep #\𝀽 'base-char) ⇒ false (typep #\𝀽 'extended-char) ⇒ true etc.