Do we always write English as we speak it?

Not always so! When we write English we are mindful that there are certain rules which have to be observed. There are rules, of course, when speaking English but to a lesser extent. Speaking the language offers the opportunity to be a less formal. For example, take this sentence: There is the woman I gave the book to. Now, this is fine when reporting the occasion orally to someone else, but if you were writing about the occasion and wanted to display a more formal style, as well as one that was grammatically correct, you would write: There is the woman to whom I gave the book. This is preferable to writing: There is the woman who I gave the book to.

When and when not to use who or whom when speaking and writing English is something upon which I will touch tomorrow (I wrote that last sentence in a very formal mode but I could have written: When and when not to use who or whom when speaking and writing English is something I will touch on tomorrow. Less formal but still correct.