#456 – Explicitly Implemented Interface Members Are Automatically Private

When you explicitly implement an interface member in a class, you make the member accessible only through objects whose type is the interface and not through objects whose type is the class.

    public class Cow : IMoo
    {
        void IMoo.Moo()
        {
            Console.WriteLine(string.Format("{0} says Moo", Name));
        }

        // rest of class here

            Cow bessie = new Cow("Bessie", 5);

            // bessie.Moo();    // Compile-time error

            IMoo viaMoo = bessie;
            viaMoo.Moo();       // OK

Because explicitly implemented interface members are not accessible via normal class instances, all explicitly implemented members are implicitly private.  These members cannot include an access modifier (either private or public).