Jquery Validation: allow only alphabets and spaces

jQuery.validator.addMethod("lettersonlys", function(value, element) {
    return this.optional(element) || /^[a-zA-Z ]*$/.test(value);
}, "Letters only please");

Use pattern: /^[a-zA-Z ]*$/

Your validation is proper. You just need to change regex /^[a-zA-Z ]*$/

$.validator.addMethod("alpha", function(value, element) {
    return this.optional(element) || value == value.match(/^[a-zA-Z ]*$/);
 });

Just leave a space or use \s in your regex:

$.validator.addMethod("alpha", function(value, element) {
    return this.optional(element) || value == value.match(/^[a-zA-Z\s]+$/);
    // --                                    or leave a space here ^^
});

Instead of the below regex:

/^[a-zA-Z]+$/

Use this:

/^[a-zA-Z\s]+$/

This will also take the space.