Compiler error · error CS1955

Non-invocable member 'X' cannot be used like a method

You added () to something that isn't a method. Nine times out of ten it's a property — Count, Length, Name — read like a field, not called like a function.

See it happen

var names = new List();
names.Add("Ada");
Console.WriteLine(names.Count());   // Count is a property — no parentheses

Fix: drop the parentheses

var names = new List();
names.Add("Ada");
Console.WriteLine(names.Count);     // property: read it, don't call it

The rule that decides it

Things that DO something are methods (with ()); things that ARE something are properties (without).

MemberProperty or method?Correct use
List<T>.Countpropertylist.Count
string.Lengthpropertys.Length
T[].Lengthpropertyarr.Length
List<T>.Add(x)methodlist.Add(5)
string.ToUpper()methods.ToUpper()

Your own members: same rule

class Person
{
    public string Name { get; set; }     // property → read as person.Name

    public string Describe()             // method → call as person.Describe()
    {
        return Name;
    }
}

Person p = new Person { Name = "Ada" };
Console.WriteLine(p.Name);               // no ()
Console.WriteLine(p.Describe());         // with ()

Related, but different

CodeMeaning
CS1955Parentheses on a non-method (property/field)
CS1061The member name doesn't exist at all
CS1501The method exists but the argument count is wrong

So if the compiler says "non-invocable", the name is right and the () is wrong. That narrows it to one character.

Frequently asked

What does CS1955 mean?

You used () on a member that is not a method — usually a property like Count or Length. Remove the parentheses.

Property or method — how do I tell?

Does it act (Add, ToUpper)? Method, with (). Does it simply have a value (Count, Name)? Property, no (). IntelliSense shows the distinction with a wrench vs. a cube icon.

Checklist