Allow comments only for author of the node and certain role I'm using Drupal 7. It is possible to disable the comment form for a specific node type for authenticated users? What hooks should I use if I want to allow only the author of the node and the administrator to post comments. The normal users (authenticated role) should only read them.

Thank you
You can probably unset the comment form using hook_form_alter on the basis on certain condition:

function MODULENAME_form_alter(&amp;$form, &amp;$form_state) {
  if ( $form_id == 'comment_form') {
    global $user;
    if (!user_access('administer nodes') {
      // Form alter here to unset comment form
      unset($form);
    } 
  }
}