There is a solution dependin on the type of field you have. Most fields will have this type of option. I'll use an example of a Text Field called "Company"
1. Find Tab-In the Object Library on the right hand side (or whereever you have it placed), you'll have the following tabs associated with a text field:
GO TO OBJECT TAB
2. Object Tab-Value- When you highlight the object tab, you'll see the 3 following tabs:
GO TO VALUE TAB
3. Type Drop-Down Menu- You'll have a few items in this tab:
- Empty Message
- Validation Pattern (Button)
- Validation Pattern Message
- Validation Script Message
PICK USER ENTERED - REQUIRED from the type drop-down menu.
Although you have no contrl over what is typed in the blank it will require that they fill in the field. Another aspect that helps control the flow of the form is to ensure the Tab Order goes in the right direction from blank to blank. Please let me know if this helps.