Include jQuery in your theme properly

gistfile1.php

add_action( 'wp_enqueue_scripts', 'sd_frontend_script_and_style' );
function sd_frontend_script_and_style() {
  wp_deregister_script( 'jquery' );
	$jquery_url = 'http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js';
	wp_register_script( 'jquery', $jquery_url, array(), null, false );
	wp_enqueue_script('jquery');
}