> thanks very much for you explanation.

You're welcome.

>
>when a modal form calls a non-modal form, does VFP run the
>two forms in separate threads then ?
>

No, VFP is not multi-threaded. But multiple forms can be running at the same time, waiting to respond to events. Non-modal forms give the user the chance to look up something in another form without closing the form they are on.