Due to both its simultaneous development in distinct countries and the absence of a single rule-making body that governs usage, the English language can often seem to lack absolute grammatical rules. Nevertheless, they do exist, despite significant differences from country to country. Part of the fun of learning English is discovering cultural, regional, and even local variations.
For those who seek an accurate as well as entertaining take on American English usage, I suggest the website Grammar Girl: Quick and Dirty Tips. Hosted by Mignon Fogarty, the site offers help not only on tricky grammar issues and confusing spelling rules but also for writing with more clarity and verve. Readers can submit questions and sign up for newsletters. There are many videos starring Fogarty and numerous other features.
Mignon Fogarty Inc. y Macmillan Holdings LLC. (2009). Quick & Dirty Tips. Recuperado el 21 de enero de 2013 de http://grammar.quickanddirtytips.com