[the] enabled of <object>

if the enabled of field "Middle Name" is true then ...
set the enabled of button "OK" to areAllFieldsFilledOut()


The enabled property controls whether an object is clickable and whether it is drawn with an inactive appearance.

Set it to false to make a button or text field unavailable for the user (e.g. because you don’t want them to run an action without having provided all the information needed to do it).

Set it to true to get a regular button, that highlights when clicked, and sends mouseDown, mouseUp etc. messages. When you create a new button, it defaults to being enabled.