for a definition of indirect object see: Indirect Object (definition)
In Scottish Gaelic, the indirect object must appear after the direct object and must be contained in a prepositional phrase as in (1). The structure paralleling the English Mary gave Bill the book, where the indirect object isn't marked with a preposition and the indirect object precedes the object is ungrammatical (2)
Thug Morag leabhar do Bhill give.Pst Morag a book to Bill 'Morag gave a book to Bill.'
*Thug Morag Bill leabhar give.Pst Morag Bill a book 'Morag gave Bill a book.'