Caught a post on digg.com overnight entitled "10 Most Misspelled Words in Blogs". The post details some of the homophones that people mix up for no good reason except that they weren't paying attention in grade one or two when you learn this stuff. Words like "their", "there" and "they're"; or "your" and "you're".

Surprisingly they left out "definitely", which I often see misspelled as "definately". But that's not what this post is about.

This post is in response to a comment on digg, where a commenter named Hypermarkalan posted this comment:

Practise= UK conventions
Practice= US conventions

Well, I can tell you that that's not the case at all, but it's actually very easy to remember which variant to use.

You know how you can advise someone, and therefore you have given them advice? The "s" variant is the verb (the "doing word") and the "c" variant is the noun (the "naming word"). You can give advice, but you advise someone. "License" and "licence" follow the same rule - you license someone to drive, but you own a driver's licence. I'm also reasonably certain that "devise" and "device" are two words that are similarly related.

It's exactly the same with "practise" and "practice". You practise doing something, and once you've done it you have practice. Again, the "s" variant is the verb, and the "c" variant is the noun.

Hope this helps you understand how to use the two words. Start practising best-practice grammar now!