why is this always 'no'?

Can anyone tell me why this always executes to 'no'? With the debugger I can clearly see values for $post_array 

if ((empty($post_array->elimination_of_uncertainty)) && (empty($post_array->technological_in_nature)) &&
            (empty($post_array->permitted_purpose)) && (empty($post_array->process_of_experimentation))) {
            $iComplete = 'no';
        } else {

        $iComplete = 'yes';
    }

proof that an old dog can learn new tricks