如果用户输入数字而不是字母，如何提示错误

Question

    <script>


 $(document).ready(function(){




var form = $("#contact_form");
var FName = $("#fname"); //Creates Variables from forms 
var FNameInfo = $("#fnameInfo");
var LName = $("#lname");
var Tele = $("#tele"); 
var Email = $("#email"); 

FName.blur(validateFName); 

form.submit (function(){

    if (validateFName & validateSName & validateTele() & validateEmail() ){ //If it passes all of these then return true 

    return true;
}else  {
            return false;
          }

    }); 

    function validateFName () {
    if (FName.val().length < 5  || FName.val == "0"){                        
            FName.addClass("error");
            FNameInfo.text("Incorrect Name");
            FNameInfo.addClass("error");
            return false; 




    }



   else {

            FName.removeClass("error"); 
            FNameInfo.text("Whats your fname" ); 
            FNameInfo.removeClass("error"); 
            return true; 
   }
    }
}); 

    </script>


   <form action="" method="get" id = "contact_form">
            <div> 
                      <label for ="name">First Name </label>
                      <input id = "fname" name = "fname" type = "text"/> 
                    <span id = "fnameInfo" > Whats your first name?</span>
           </div>
            <div>
               <label for ="lname">Last Name </label>
               <input id = "lname" name = "lname" type = "text"/> 
               <span id = "lnameInfo" > Whats your last name?</span>
            </div>

            <div>
               <label for ="tele">Telephone </label>
               <input id = "tele" name = "tele" type = "text"/> 
               <span id = "fnameInfo" > Telephone</span>
            </div>

            <div>
               <label for ="email">email </label>
               <input id = "email" name = "email" type = "text"/> 
               <span id = "fnameInfo" > Whats your last email?</span>
            </div>

            <div>
               <input id = "send" name = "send" type = "submit" value = "send"/> 
            </div>


        </form>

好的，对于名字我希望用户在输入数字而不是字母时显示错误。我需要打开表单以确定错误，因此不会应用任何限制，只有在用户输入数字时出现错误