Controller not recieving my parameter

[eluser]Joures[/eluser]
So i'm on my second day developing with CI and ran in to a little problem
i can't solve.

So, i got this anchor leading to localhost/folder_containing_ci/subcategories/display/1
where the number 1 is and id from the parent of that subcategory.

The thing is, when i click the link this error occurs: Undefined property: Subcategories::$id
And the display function looks like this:

Code:

<?php

class Subcategories extends Controller {
    
    public function display($id) {
        
     // fetching subcategories depending on $id
    }
}

Everywhere i look it says 'CI will pass down the parameter automatically'.

What am i doing wrong?