I am doing a technical and scientific writing. I have been confused by this for a long time. Basically, there are two case.

  1. A well-known phrase with its abbreviation. e.g. Global Positioning System (GPS). Should I write "Global Positioning System (GPS)" or "global positioning system (GPS)"?
  2. A self-coined phrase with its abbreviation. e.g. Augmented Filter Subsystem (AFS). Should I write it as "Augmented Filter Subsystem (AFS)" or "augemented filter subsystem (AFS)"?

Does it really matter? I am trying to do the best that I can. Which one is more conventional?

  • 1
    I've had to do a lot of "technical spec" writing over the years, within which context it's often useful to coin new expressions. In the case of something like "This product features an Augmented Filter Subsystem (AFS)", I would normally capitalise it like that (and include the bracketed abbreviation) on the first reference. I think using such a convention makes it just that little bit easier for the reader to recognise what the abbreviation refers to. Nov 16, 2013 at 18:53

4 Answers 4


The US Department of Defense began operation of the Global Positioning System back in 1993, following development of the Navigation System with Timing and Ranging (NAVSTAR) in the early 1970's. Today, GPS, as we know it, is owned by the US Government, and managed by the US Air Force. All of these organisations refer to Global Positioning System. Furthermore, the GPS Standard Positioning Service (SPS) Performance Standard document released by the administering authority refers to the capitalized version. So, I don't believe there is an argument about that one.

For other self-coined phrases, it may be a different case. Take for example ATM, ABS and DIY - there is no case for capitalizing the words as they are simply abbreviations of a common phrase. If, however, you are wanting to identify some specialized item (or are a cunning marketer), you might want to capitalize the phrase. I think "Augmented Filter Subsystem (AFS)" has a better ring to it; far more worthy of a patent or higher dollar charge.


"Global Positioning System" is the proper name given by the U.S. Department of Defense to its satellite navigation system. It should always be capitalized, not because it's well-known per se but because it's a proper name. To avoid confusion, you should never refer to a different satellite navigation system—or to such systems in general—as global positioning systems.

As for self-coined phrases, it's basically your call. Acronyms and initialisms are almost always capitalized, but there's no requirement that the phrase expanded from an acronym must be capitalized: "GDP" expands to "gross domestic product" in a sentence, for example. But if it's self-coined, it's yours and you can do what you want with it.

If you want my advice, though, one thing I've learned from 15 years of technical writing is that programmers and engineers like to capitalize way too many things. As a general rule of thumb, if you're dealing with words that are not normally capitalized (such as "augmented," "filter," and "subsystem"), leave them uncapitalized unless they already form a proper name or will be used in (*shudder*) marketing materials.


I think that acronyms should be capitalized (e.g., DIY), even though they aren't proper nouns, because it identifies them as acronyms. After a few decades, though, some fall into common use, so today we write 'radar", even though it was originally RADAR.

The GPS is a specific thing (proper noun), like the Grand Canyon or Angkor Wat.

Here's another example from IT: " RAID stood for "redundant array of inexpensive disks," but now it usually refers to a "redundant array of independent disks."

Capitalize the acronym, not the words.


It doesn't matter, but it seems to me that "Global Positioning System" is more widely accepted than the "global positioning system"

  • Global Positioning System is a proper name. You do not capitalize your own name, so I understand why it wouldn't matter to you personally, but it very much does matter to others.
    – RegDwigнt
    Nov 16, 2013 at 19:35

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