validate_comments.php

<?php
/*
Add to functions.php
*/
function comment_validation_init() {
	if(is_singular() && comments_open() ) { ?>
	<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.13.1/jquery.validate.min.js"></script>
	<script type="text/javascript">
	jQuery(document).ready(function($) {
	$('#commentform').validate({
	 
	onfocusout: function(element) {
	  this.element(element);
	},
	rules: {
	  author: {
	    required: true,
	    minlength: 2
	  },
	  email: {
	    required: true,
	    email: true
	  },
	  comment: {
	    required: true,
	  }
	},
	messages: {
	  author: "Please enter in your name.",
	  email: "Please enter a valid email address.",
	  comment: "Message box can't be empty!"
	},
	errorElement: "div",
	errorPlacement: function(error, element) {
	  element.after(error);
	}
	});
	});
	</script>
	<?php
	}
}
add_action('wp_footer', 'comment_validation_init');