Guardian Style Guide author David Marsh set out to master perfect grammatical English – but discovered that 'correct' isn't always best. Here are the 10 grammar laws you no longer need to check 'To go boldly?' 'Negative, Captain, it's fine to split an infinitive.' Photograph: Cine Text/Sportsphoto Ltd/Allstar Every situation in which language is used – texting your mates, asking for a pay rise, composing a small ad, making a speech, drafting a will, writing up an experiment, praying, rapping, or any other – has its own conventions. You wouldn't expect a politician being interviewed by Kirsty Wark about the economy to start quoting Ludacris: "I keep my mind on my money, mo...