Why do we capitalize "I"?

Why do we capitalize the first-person pronoun, I? The short answer is because we do. But that’s not a very satisfactory answer. Even though it feels natural to English speakers, capitalizing I is unusual. In fact, English is the only language that does. Germanic and Romantic languages typically have some conventions for capitalizing proper nouns, like Deutschland (in German) or Place de la Concorde (in French), but English is the only one that selfishly insists on capitalizing the personal pronoun. We do not, you will recall, even capitalize we.

It turns out that this unusual convention was a bit of an accident. In Old and Middle English, the word for “I” was closer to its German cousin, “ich,” and it was often spelled “ic.” At this point, the word was not capitalized. However, the pronunciation changed over time and so did the spelling, losing the consonant c.

At first, the new word, i, was left lowercase. However, it began to grow taller than other words. It grew for a silly reason: a single letter looks bad. Look at it: i. How sad. By the time Chaucer wrote The Canterbury Tales in the late 1300s, I, the personal pronoun, was slightly taller than its lowercase equivalent. From that point on, it was typically capitalized.

The only other accepted single-letter word in English, a, is a larger presence on the page. Its appearance isn’t as offensive as the thin i.

Today, though, some of us are regressing. In e-mails and instant message conversations, capitalization conventions are backsliding.

http://blog.dictionary.com/whycapitali/