Skip to main content

How to Resolve Error "CS0175: Use of keyword 'base' is not valid in this context" in C#

The Compiler Error CS0175 is a context restriction error. The message reads: "Use of keyword 'base' is not valid in this context".

In C#, the base keyword is used to access members of the parent class that might be hidden or overridden in the current class. However, C# does not allow you to use base just anywhere. There are specific syntactic structures—most notably Object Initializers, Anonymous Types, and certain Query Expressions—where the compiler cannot correctly resolve the reference to the parent class members.

This guide explains why these restrictions exist and how to work around them.

Understanding the 'base' Keyword Context​

The base keyword is implicitly tied to the this pointer (the current instance), but it tells the runtime to look up the method or property in the Parent's Virtual Method Table (vtable) instead of the Child's.

Syntactic structures like Object Initializers (new Obj { ... }) are "syntactic sugar." Under the hood, they are often translated into temporary assignments. In these specific transition zones, the compiler's logic for resolving base access is not supported, often because the object is technically still under construction or the scope is isolated.

Scenario 1: Object Initializers​

This is the most common cause of CS0175. You are creating an instance of a class and trying to initialize its properties using values from the base class directly inside the curly braces {}.

Example of error​

You want to create a Child object and set one of its properties to match a value found in the Parent.

public class Parent
{
    public int DefaultScore { get; set; } = 100;
}

public class Child : Parent
{
    public int CurrentScore { get; set; }

    public void Reset()
    {
        // ⛔️ Error CS0175: Use of keyword 'base' is not valid in this context
        // You cannot use 'base' inside the object initializer braces.
        Child c = new Child 
        { 
            CurrentScore = base.DefaultScore 
        };
    }
}

Solution: Assign Outside or Use Local Variable​

You must move the base access outside of the initializer block.

Option A: Local Variable (Recommended) Capture the value first, then use the variable.

public void Reset()
{
    // 1. Capture the value
    int defaults = base.DefaultScore;

    // 2. Use the variable
    // ✅ Correct: Variable access is valid here
    Child c = new Child 
    { 
        CurrentScore = defaults 
    };
}

Option B: Constructor Logic If this logic is common, move it to the constructor of the Child class.

public class Child : Parent
{
    public Child()
    {
        // ✅ Correct: 'base' is perfectly valid inside a constructor
        this.CurrentScore = base.DefaultScore;
    }
}

Scenario 2: Anonymous Types​

When creating an Anonymous Type (using new { ... }), you are projecting data into a brand new, compiler-generated class. This new class does not inherit from your current class; therefore, it has no concept of your base class.

Example of error​

Trying to project a parent method's result directly into an anonymous object.

public class Parent
{
    public string GetCode() => "A-123";
}

public class Child : Parent
{
    public override string GetCode() => "B-456";

    public void CreateData()
    {
        // ⛔️ Error CS0175: Use of keyword 'base' is not valid in this context
        // The anonymous object definition cannot resolve 'base'.
        var data = new 
        { 
            Id = 1, 
            Code = base.GetCode() 
        };
    }
}

Solution: Capture in Variable​

Just like with object initializers, you must extract the value into a local variable first.

public void CreateData()
{
    // 1. Execute base logic and store it
    string parentCode = base.GetCode();

    // 2. Use the simple variable
    // ✅ Correct
    var data = new 
    { 
        Id = 1, 
        Code = parentCode 
    };
}
note

Why this happens: Anonymous types are generated as distinct internal classes. Trying to call base.GetCode() inside their definition is syntactically confusing because the "base" of the anonymous type is System.Object, not Parent.

Conclusion​

CS0175 is a limitation of specific C# syntax structures. The compiler prevents base usage where the scope of "the parent object" is ambiguous or unsupported.

  1. Check Curly Braces: Are you inside new MyClass { ... } or new { ... }?
  2. Extract Variables: The universal fix is to declare a local variable (var x = base.Value;) immediately before the problematic block, and use x inside the block.

Table of Contents