Try something like this:

$rules = [
	// Validation rules
	"firstname"	=> "required",
	"lastname"	=> "required",
	"phone"		=> "required"
];

$messages = [
	// Custom error messages
	"firstname.required"	=> "Please enter your first name.",
	"lastname.required"		=> "Please enter your last namer.",
	"phone.required"		=> "Please enter a phone number where you can be reached."
];	

if(Input::get('action') == "create") {  // Example, check if the user is beeing created
	// Add new rules
	$rules["email"]				= "required|email";
	$messages["email.required"]	= "Please enter an email address.";
	$messages["email.email"]	= "Please enter a valid email address.";
}

$validator = Validator::make(Input::all(), $rules, $messages);

ok thanks