pre_get_posts_change_order

<?php

/* It changes the order only for the main blog page */
if ( ! function_exists( 't_n_order' ) ) :
add_filter( 'pre_get_posts', 't_n_order' );
function t_n_order( $query ) {
    if($query->is_home)
        $query->set( 'order' , 'asc' );
    return $query;
}
endif;

/* It changes all over the site */
if ( ! function_exists( 't_n_order' ) ) :
add_filter( 'pre_get_posts', 't_n_order' );
function t_n_order( $query ) {
    $query->set( 'order' , 'asc' );
    return $query;
}
endif;
/* It changes the order for the main blog page, categories, tag pages and the other post archives */
if ( ! function_exists( 't_n_order' ) ) :
add_filter( 'pre_get_posts', 't_n_order' );
function t_n_order( $query ) {
    if($query->is_home || $query->is_archive)
        $query->set( 'order' , 'asc' );
    return $query;
}
endif;