How do I use arguments together with bash aliases
You can't pass arguments to aliases. Aliases are just text substitutions without further logic. 

But you can use shell functions to achieve the same result:

function pman() {
    if [ -x /usr/bin/open ]; then
        man -t "$1" | open -f -a Preview
    else
        man "$1"
    fi
}


The if-then-else part is there just to make sure it also works on non-OSX systems.

To define a function, just include the definition from above into your ~/.bash_profile. Usage is identical to aliases or any other command: pman ls.

As @stuffe pointed out in a comment keeping aliases/functions in a separate file has its advantages (especially it allows you to re-read your aliases/functions into the current shell without executing any setup stuff from .bashrc or .bash_profile). To do this, create a separate file called .alias, .functions or similar and add

test -e ~/.alias &amp;&amp; . ~/.alias


to .bashrc or .bash_profile.