Recently a friend contacted me and asked, ‘Is it am and pm, or a.m. and p.m., or A.M. and P.M. or AM and PM?’
Turns out, it doesn’t really matter which set of abbreviations you choose when you’re talking about time. What matters is that you are consistent. So if you choose ‘am’, then you use ‘pm’. If you choose ‘A.M.’, then it’s also ‘P.M.’, and so it goes on …
But not all abbreviations come with this degree of flexibility. It’s not so much that there are ‘rules’. It’s more that people have agreed, over time, on some common usages.
Here are a few guidelines to help you out:
- For job titles where the first few letters are written and the rest of the word omitted, we usually put a full stop at the end—Rev. for Reverend, Prof. for Professor
- If an abbreviation uses the first and last letters of a word, we usually OMIT the full stop—Dr for Doctor, Ltd for Limited
- Many abbreviations which used to take include full stops, have lost those in modern usage—UK for United Kingdom (not U.K.), USA for the United States of America (not U.S.A.), BBC for the British Broadcasting Corporation (not B.B.C.), NHS not N.H.S., CD not C.D., D J Trost not D.J. Trost, etc.
- When you are using an abbreviation which is likely to be unfamiliar to your readers, spell out the full word or words first and include the abbreviation in brackets, then use the abbreviation for the rest of the document.
The important thing is to be consistent. I know I mentioned the idea of using a style guide in a previous blog post. If you are preparing a style guide for your organization, it’s important to include abbreviations in it.
Oh, and another thing. If your sentence ends with an abbreviation and you’ve decided to use full stops, only put one full stop, not two.
Hope this helps.