Instead of the below regex:

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

Use this:

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

This will also take the space.

If you include the additional methods file, here's the current file for 1.7: http://ajax.microsoft.com/ajax/jquery.validate/1.7/additional-methods.js

You can use the lettersonly rule :) The additional methods are part of the zip you download, you can always find the latest here.

Here's an example:

$("form").validate({
  rules: {
    myField: { lettersonly: true }
  }
});

It's worth noting, each additional method is independent, you can include that specific one, just place this before your .validate() call:

jQuery.validator.addMethod("lettersonly", function(value, element) {
  return this.optional(element) || /^[a-z]+$/i.test(value);
}, "Letters only please"); 

To match the terms:

• Expression can start only with a letter
• Expression can contain letters or spaces

You need to use this regex expression:

/^[a-z][a-z\s]*$/

So in your js it should be:

jQuery.validator.addMethod("letterswithspace", function(value, element) {
    return this.optional(element) || /^[a-z][a-z\s]*$/i.test(value);
}, "letters only");

Explanation

1. ^[a-z] means start with one letter
2. [a-z\s]*$ means after accept zero or more letters or spaces

Valid sentence

If you want a valid sentence structure:

• Expression can start or end only with a letter
• Expression cannot contain consecutive spaces

use:

/^([a-z]+\s)*[a-z]+$/

By the way

2. These regex expressions do not accept capital letters. To add capital letters support instead of a-z use a-zA-Z

I found the answer after some search.

we can use below regex to achieve this.

/^([\s.]?[a-zA-Z]+)+$/

Complete jQuery function:-

<script>
    $(document).ready(function () {
        $("input[type='text']").each(function () {
            $(this).blur(function (e) {                  
                if (Validate(this.id)) { }
                else { alert('invalid input'); }
            });
        });

        function Validate(evt) {
            var isValid = false;
            var regex = /^([\s\.]?[a-zA-Z]+)+$/;              
            isValid = regex.test($("#" + evt).val());
            return isValid;
        }
    });
</script>

Simply add a custom validator, and use it like this:

jQuery.validator.addMethod("accept", function(value, element, param) {
  return value.match(new RegExp("." + param + "$"));
});

Only numbers:

rules: {
  field: { accept: "[0-9]+" }
}

Only letters

rules: {
  field: { accept: "[a-zA-Z]+" }
}

You need to add the whitespace character (\s) to your Regex:

jQuery.validator.addMethod("lettersonly", function(value, element) {
    return this.optional(element) || /^[a-z\s]+$/i.test(value);
}, "Only alphabetical characters"); 

You can use custom validator method and specify your custom validation there.Whenever user clicked on submit button this will get called and will validate the input according to the rules defined in it .

In below code i have use regex to match user input . i.e :

^ : It represents start of string .
\w : It matches any word character (equal to [a-zA-Z0-9_])
(space or ) \s : It matches any space, tab or newline character.
$ : It represent end of string .
.test(value) :It match between a regular expression and a specified string and return true or false.

Demo code :

$(document).ready(function() {
  //add this custom methid
  $.validator.addMethod("alphanumeric", function(value, element) {
    //test user value with the regex
    return this.optional(element) || /^[\w ]+$/i.test(value);
  }, "Letters, numbers only please");

  $('#myform').validate({ // initialize the plugin
    rules: {
      field: {
        required: true,
        alphanumeric: true
      }
    },
    submitHandler: function(form) { // for demo
      alert('valid form submitted'); // for demo
      return false; // for demo
    }
  });


});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.19.2/jquery.validate.min.js
"></script>
<form id="myform">
  <input type="text" name="field" />
  <br/>
  <input type="submit" />
</form>

    jQuery.validator.addMethod("alphanumericspecial", function(value, element) {
        return this.optional(element) || value == value.match(/^[-a-zA-Z0-9_ ]+$/);
        }, "Only letters, Numbers & Space/underscore Allowed.");

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

    jQuery.validator.addMethod("alphanumeric", function(value, element) {
return this.optional(element) || value == value.match(/^[a-z0-9A-Z#]+$/);
},"Only Characters, Numbers & Hash Allowed.");

U can create functions easily like this bro..