We all have our favourites when it comes to literature. Some are fans of the romantic novel, others of science fiction; some of historical accounts, some of adventure novels - and all points in between. The common factor is the use of the language; building scenes, characters, situations etc. Sentences can often be long and flowery. Not so in advertising copy.

What we need in advertising copy is text that will grab your attention. Quickly. Invariably this means short sentences, which don't always have to be grammatically correct. Take for example "Beanz Meanz Heinz". Ever heard that one? One of the simplest and best advertising phrases of the last 50 years. Bet you can even remember the preceding phrase? It was written by Mo Drake, then the Deputy Creative Director of Young & Rubicam, and it ran for over 30 years.

Several people have offered formulae to measure the readability of copy. C R Has gave us a formula which evaluated the effectiveness of advertising copy based on the relative number of verbs to nouns used. Mr R Gunning devised an index to look at the length of sentences, and the percentage of words used with three or more syllables in them. Even more obscurely, the Dale-Chall index was based on used a vocabulary of 3,000 words that were most easily understood by 80% of American schoolchildren in the fourth grade. These formulae are not widely used these days, but the overall message is clear, and has not really changed - short sentences, and uncomplicated words.

As far as readability tests go, perhaps the best one to use as a guide is the one developed by a man named Rudolf Flesch. His formula is based on 4 main points:
1.The average number of words per sentence (short sentences)
2.Average word length (uncomplicated words)
3.Percentage of personal words
4.Percentage of personal sentences

Personal words are included to create greater interest - to get the reader to empathise with the writer. Point 4 just means don't overdo it. To get an average word length, take a sample of 100 words, and count the number of syllables. The formula is complex, and should you want to try it out, Wikipedia has it under "Flesch Reading Ease". Personally I think trying to evaluate a piece of copy by a mathematical formula is a step too far, but the gist keeps coming back. Short sentences, simple words.

In the final analysis, it is of course the results of the mailshot / email campaign that will be the judge of how good the copy is. By no means is it the only factor in the success of the campaign, but every so often you'll get feedback that will let you know if you are on the right track. Keep writing, keep it impactful, and keep it simple.