French orthography encompasses the spelling and punctuation of the French language. It is based on a combination of phonemic and historical principles. The spelling of words is largely based on the pronunciation of Old French c. 1100–1200 CE and has stayed more or less the same since then, despite enormous changes to the pronunciation of the language in the intervening years. This has resulted in a complicated relationship between spelling and sound, especially for vowels, a multitude of silent letters, and a large number of homophones (e. g. , saint/sein/sain/seing/ceins/ceint (all pronounced [sɛ̃]), sang/sans/cent (all pronounced [sɑ̃])). Later attempts to respell some words in accordance with their Latin etymologies further increased the number of silent letters (e. g. , temps vs. older tens – compare English "tense", which reflects the original spelling – and vingt vs. older vint). Nevertheless, there are rules governing French orthography which allow for a reasonable degree of accuracy when pronouncing French words from their written forms. The reverse operation, producing written forms from a pronunciation, is much more ambiguous.