I was lead to believe that there were no differences between aliases in zsh and bash, however that appears to not be the case. I had an alias that would help me familiarize myself with the command line utilities available to me, but after copying it over to the new `.zshrc` of mine, it fails to work. I have confirmed that it's not an error by changing the alias, which resolved the issue. 

The command is aliased to `?`. Why can I not use `?` when creating an alias?

    alias ?='pwd'
    alias ?='echo hello'

amongst others have been attempted. No alias mapped to `?` has worked, as mentioned.

It is located in the `~/.zshrc` file. 
I copied it from my .bashrc, as I have just decided to try zsh out.