- A review of all third-order, two-dimensional technical theories of plates is presented and their equivalence is established. All third-order theories published during the last two decades are shown to be based on the same displacement field, contrary to the claims by many authors. Consequently, all variationally derived plate theories are a special case of the third-order plate theory published by the author in 1984. A consistent-strain, third-order, displacement field is proposed herein and associated, variationally consistent, theory is developed. 1990.