title: if can? in Ruby on Rails
body: <p>In a Ruby on Rails application that I inherited from someone, I have code that looks like so</p>
  
  <pre><code>&lt;% if can? :create, :objects %&gt;
  &lt;%= link_to 'Add New Object', new_object_path %&gt;
  </code></pre>
  
  <p>This web application has a login and users have different permissions that are defined in a table called <code>groups_roles</code> (which groups (ex. admin, user) have which roles (ex. add new objects))</p>
  
  <p>I want to add new permissions, so where do I do that at? Where are these things defined? How does Ruby know which table to get the different permissions from, and how does it know what <code>:create</code> and <code>:objects</code> are in the code above?</p>