When should you use a field rather than a property?

Question

Can anyone clearly articulate when you use a field and when to use a property in class design?

Consider:

public string Name;

Or:

Answer 1

Using properties you can control it's security:

public string Foo { protected get; private set; }

Properties gives easy way to raise events:

public string Foo
{
  get { return _foo; }
}
set
{
  bool cancel = false;
  if(BeforeEvent != null) // EventHandler BeforeEvent
  {
    CancelEventArgs e = new CancelEventArgs();
    BeforeEvent(this, e);
    cancel = e.Cancel;
  }
  if(!cancel)
  {
    _foo = value;
    if(AfterEvent != null) // EventHandler AfterEvent
    {
      AfterEvent(this, new EventArgs());
    }
  }
}

Also I often use code like this:

string Foo
{
  set
  {
    IsFooSet = value != null;
  }
}

bool IsFooSet
{
  get { return _isFoo; }
  set
  { 
   _isFoo = value;
   if(value) // some event raise or controls on form change
  }
}