Unable to keep array element downcase that is found in include? method

I am a Ruby Newbie and I'm having some trouble with my Title class below. I have the first two logical requirements met, but the third one I am having some trouble with. I have researched on StackOverFlow and Google and I have seen how you can use the if structure in the map method and I'm not sure why this isn't working for me. Can anyone offer any assistance/guidance?

1. It is successfully taking an all lower case string like "the united states" and making each 1st letter in each word capitalized(The United States)in the string.


2. 
   

   It is successful in taking a camel case string like "ThE UnIted STatEs" and making it "The United States".

   
   


3. 
   

   I am trying to add the additional logic where if the string is "the", "The", "of", "Of" it does not capitalize it. I received the error of: wrong number of arguments (2 for 1). Is there another way I can implement this logic?

   
   

The attempted map logic to the Title Class that did not work | Error received: wrong number of arguments (2 for 1)

class Title
 attr_accessor :string
 def initialize(string)
 @string = string
end

def fix
 string2 = string.split(" ").map{ |string| string.capitalize }.join(" ")
string2.split(" ").map{ |string| (string.include?("of","Of","the","The") ?   string.downcase : string.capitalize) }.join(" ")

end

end

Title Class that works fine for #1 & #2

class Title
 attr_accessor :string
 def initialize(string)
 @string = string
end

def fix
 string2 = string.split(" ").map{ |string| string.capitalize }.join(" ")
 end
end