validate a form when using modal?

I try to make a form validation, but if I hit submit, the form disapears before giving me the feedback:

<div class="ui first coupled modal">
<i class="close icon"></i>
<div class="header">
tell me something
</div>
<div class="content">
<form class="ui form" method="post" action="/msg">
    <h4 class="ui dividing header">What do you think</h4>
    <div class="field">
      <label><i class="write icon"></i></label>
      <textarea name="txt" class="field" placeholder="write something" required></textarea>
      <input class="ui green button" type="submit" value="gtt"/>
    </form>
  </div>
</div>

<div class="ui small second coupled modal">
<div class="header">
<i class="red heart icon"></i>
</div>
<div class="content">
  <div class="description">

    <h1>Thank you</h1>

  </div>
</div>
<div class="actions">
  <div class="ui approve inverted blue button">
    <i class="checkmark icon"></i>
    Bye ^_^
  </div>
</div>

The JS:

 function contact(){
         $('.coupled.modal')
          .modal({
            allowMultiple: false
          })
        ;
        // attach events to buttons
        $('.second.modal')
          .modal('attach events', '.first.modal .button')
        ;
        // show first now
        $('.first.modal')
          .modal('show')
        ;    
    }