[jwilk]

Instead of which(1), you could use type, which is aware of builtins and aliases:

  $ type cd
  cd is a shell builtin

[chaosfox]

if you use zsh on the other hand..

  % which which
  which: shell built-in command

[aidenn0]

command is also useful for this sort of thing (with the -v and -V options). It can also be used to ignore shell functions and aliases (without options) so:

  $ alias cd=ls
  $ cd foo
   <lists contents of foo>
  $ command cd foo
   <changes to directory foo>