A while ago I was pondering the meaning of some of the terms that the KJV uses, such as "thee", "ye", "eth" (the suffix). I found this article, entitled The KJV's Archaic Language, which explains what these these words and suffixes mean. I wont write too much in this blog, as it's all covered in the article.
Many of these terms tell you about whether the phrase is meant in a singular or plural sense, and also whether it's said in the first, second or third person. Although you can most often correctly guess these things in a modern translation such as the NIV, sometimes this depth of language is needed. One striking example pointed out in the article is John 3:12:
(KJV) If I have told you earthly things, and ye believe not, how shall ye believe, if I tell you of heavenly things?
(NIV) I have spoken to you of earthly things and you do not believe; how then will you believe if I speak of heavenly things?
In the KJV English, "you" and "ye" are plural, not singular. Therefore in this verse Jesus was actually referring to a group of people, probably the Pharisees or the Israelite nation, despite Nicodemus being the only person present.
Anyway, I'll let you go and read the article for yourself. In case you missed it, here's the link: The KJV's Archaic Language.