JQuery :: Handling Variables Success With $.ajax?

This is the exemplar I've been using for my $.ajax requests to my php script.

$.ajax({ type: 'GET', url: 'getDetails.php', data: { id: 142 }, success: function(data) {
// grabbed some data! };
});

I'm working with a few more variables than this, I'm working with 3 variables. What I'm wondering is should I use json_encode() on the php side. I will be using php validations, so I may return error messages in an array. How do I check whether I have error messages or true value.

I'd like to send in an associative array so I can have email = "error"; amongst a few others. So if email is the only one with error I will .append a message to the correct div id.