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    <p>Let's first make sure that I am interpreting your question correctly. You have classes defined as above. You are instantiating an instance of <code>A</code> and invoking a method <code>example</code> that <code>A</code> inherits from the base class. You want to know if it's possible for the call <code>this.AsAString()</code> in the method <code>Letter.Example</code> to invoke the base implementation of <code>AsAString</code> rather than the derived implementation.</p> <p>First, let's understand why with <code>example</code> defined as above, invoking <code>Letter.example</code> via an instance of <code>A</code> (e.g., <code>new A().example</code>) will cause <code>A.AsAString</code> to be invoked. From the specification (§7.4.4):</p> <blockquote> <p>The function member implementation to invoke is determined:</p> <p>If the compile-time type of E is an interface, the function member to invoke is the implementation of M provided by the run-time type of the instance referenced by E. This function member is determined by applying the interface mapping rules (§13.4.4) to determine the implementation of M provided by the run-time type of the instance referenced by E.</p> <p>Otherwise, <strong>if M is a virtual function member, the function member to invoke is the implementation of M provided by the run-time type of the instance referenced by E. This function member is determined by applying the rules for determining the most derived implementation (§10.6.3) of M with respect to the run-time type of the instance referenced by E.</strong></p> <p>Otherwise, M is a non-virtual function member, and the function member to invoke is M itself.</p> </blockquote> <p>So now let's consider your situation. You have an instance <code>a</code> of a class <code>A</code> that derives from <code>Letter</code>. You have invoked a method named <code>example</code> via the syntax <code>a.example()</code>. This will invoke <code>Letter.example</code> which has definition:</p> <pre><code>public void example() { this.AsAString(); } </code></pre> <p>This will invoke <code>Letter.AsAString</code>. But, <code>Letter.AsAString</code> is declared <code>virtual</code> and therefore, by the bolded rule above, the method that is invoked is <code>A.AsAString</code> because <code>this</code> is of type <code>A</code>, <code>A</code> derives from <code>Letter</code>, and <code>A</code> provides an <code>override</code> of <code>Letter.AsAString</code>.</p> <p>Now, if you change the definition of <code>A.AsAString</code> so that it hides the base implementation using the <code>new</code> modifier</p> <pre><code>public new void AsAString() { Console.WriteLine("A"); } </code></pre> <p>then <code>a.example</code> will cause the base implementation to be used and you will see the output <code>???</code> as you desire. This is because, by the rule above, the most derived implementation of <code>Letter.AsAString</code> (i.e., the most derived type in the hierarchy of <code>A</code> that provides a definition of the <code>virtual</code> method <code>AsAString</code>) is the base implementation. The <code>new</code> modifier allows <code>A</code> to have a method named <code>AsAString</code> with the same signature as <code>Letter.AsAString</code> but it is not a <code>virtual</code> method.</p> <p>Please let me know if I am interpreting your question incorrectly, or if any of the above requires clarification.</p>
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