Differences between American English and British English spelling came about mainly as the result of one man. Noah Webster (1758–1843) wrote a "Grammar", a "Spelling" book, and finally an "American dictionary of the English language". In the course of this, he proposed a number of simplifications in spelling. In his dictionary, he chose "s" over "c" in words like "defense", he changed the "re" to "er" in words like "center", he dropped one of the Ls in "traveler". At first he kept the u in words like colour or favour but dropped it in later editions. He also changed "tongue" to "tung": that did not stick. His main reason was to help children learn to read and write. Webster's dictionary contained seventy thousand words, of which twelve thousand had never appeared in a published dictionary before.