Why Is MyBase.MyBase Not Allowed?

In Visual Basic .NET, C#, and Java access is resticted to the direct base class. The main reason for this is that allowing access to a class’ grand-base could lead to inconsistencies in an object’s state. The sample below illustrates this problem:

Public Class A
    Private m_Sum As Integer

    Public Overridable Sub Add(ByVal Number As Integer)
        m_Sum += Number
    End Sub
End Class

Public Class B
    Inherits A

    Private m_Checksum As Integer

    Public Overrides Sub Add(ByVal Number As Integer)
        m_Checksum = …
    End Sub
End Class

Public Class C
    Inherits B

    ' Objects of type 'C' are objects of type 'B' too.  'B' guarantees that the
    ' checksum will be set properly.  If there was a way to call ' 'A''s 'Add'
    ' method directly, the checksum set in 'B' would not be updated and thus the
    ' class' state would be inconsistent.
End Class

MyBase.MyBase could be used to bypass code that is required by the class hierarchy, for example, if the derived class calls a function defined in its grand-base class directly, bypassing a base function, where the base function is needed for the entire class hierarchy to work correctly.