Again... YOU REALLY DON'T WANT TO DO THIS.

Names are *NOT* unique. I once worked with Dr. Lawrence David Wise, Ph.D. and
his colleague, Dr. Lawrence David Wise, Ph.D.; I know three people name Fred
Brown.

It will *not* prevent invalid duplicates from being added to the database, if
one gets entered with an abbreviated or missing middle name.

It *will* prevent valid records from being added to the database (unless the
data entry person gets around the restriction as above) if you happen to have
two records for people who happen to share a name.

You can *check* (not prevent) the addition of duplicates by using the Form's
BeforeUpdate event to look up names in the form's recordsource query and
alerting the data entry person of the duplication.

            John W. Vinson [MVP]

From the Access help file:

In situations where you can't guarantee the uniqueness of any single field,
you may be able to designate two or more fields as the primary key. The most
common situation where this arises is in the table used to relate two other
tables in a many-to-many relationship. For example, an Order Details table
can relate the Orders and Products tables. Its primary key consists of two
fields: OrderID and ProductID. The Order Details table can list many
products and many orders, but each product can only be listed once per
order, so combining the OrderID and ProductID fields produces an appropriate
primary key.

Each product can be listed only once per order.
Another example would be an inventory database that uses a field part number
of two or more fields (part and subpart).
If you are in doubt about whether you can select an appropriate combination
of fields for a multiple-field primary key, you should probably add an
AutoNumber field and designate it as the primary key instead. For example,
combining FirstName and LastName fields to produce a primary key is not a
good choice, since you may eventually encounter duplication in the
combination of these two fields.
In a multiple-field primary key, field order may be important to you. The
fields in a multiple-field primary key are sorted according to their order
in table Design view. You can change the order of the primary key fields in
the Indexes window.

Aaron Kem.pf is posting under a new alias.