When the source code of software is freely available, we say it is "open source".

When the source code of software is not freely available, we say it is "closed source".

Why do we not use "close source", given that it would more closely parallel "open source"?

Or would it not?

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    The adjective "closed" means "not open", the past participle of "to close" is "closed". This is formed differently to open, whereby the adjective is "open" and the past participle is "opened". The adjective "close" means "near by".I can't be bothered to find sources right now, hence a comment rather than an answer.
    – AndyT
    Oct 5, 2016 at 11:02
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    As a programmer, I can assure you that it wouldn't matter what the grammatical basis was for the difference -- once enough programmers say it one way it stays that way
    – Jeutnarg
    Oct 5, 2016 at 16:36
  • As a point backing Jeutnargs statement: note that referrer in http is misspelled. And is required to be in every conforming implementation. en.wikipedia.org/wiki/HTTP_referer Oct 5, 2016 at 18:14
  • This question was just put on hold as "off topic" for this site. Not sure why, especially given all the upvotes. Would it be more appropriate for English Language Learners SE? Oct 5, 2016 at 18:32

2 Answers 2


I don't see a problem with the phrase "closed source". "Closed" means "not open". The opposite of "the door is open" is "the door is closed", not, "the door is close". Similarly, there is "open mind" and "closed mind", etc. ("Close" can also mean "nearby", which is not the intended meaning here.)

One of the definitions for closed in Collins is "restricted; exclusive". When we accept this definition, "closed-source software" is software where access to the source code is restricted to those who own the code's copyright (or that subset of employees who actually contribute to it).

Another definition from Collins is "blocked against entry; shut". Closed-source software is kept in source code repositories that block access from the outside world.

"Opened" would assume that the source code was previously "closed". You can find instances of the phrase opened source software on the web, but it is not clear whether it always refers to software that was previously proprietary. The phrase "open-source software" is more common.

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    Those extrapolations from Collins are very helpful. Thank you Christophe. Oct 5, 2016 at 11:08
  • @RockPaperLizard An additional insight. "Opened" is hard to verbally distinguish from "open". And klōs is hard to verbally distinguish from klōz. This is why "open" is the adjective (easier to say than "opened"), and "closed" is the opposing adjective ("close" is ambiguous). Oct 5, 2016 at 14:59

"Open" is an adjective, and "closed" is the opposite, so "closed source" does indeed parallel "open source".

"To close" is the opposite of the verb "to open".

  • Thanks Paolo. Can you expand your answer to explain why "opened source" is not used? Oct 5, 2016 at 11:06
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    "Opened" is not an adjective, it is the past tense of "to open," something that has been opened is open. "Closed" is both an adjective and the past tense of "to close" Oct 5, 2016 at 12:58
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    Tenses and verb/adjective differences is a good way to answer the question. Note: "Opened" can be used adjectivally, for example as the opposite of "sealed", but like "sealed" and "shut", carries a suggestion that the object was once in a different state. "Open" and "Closed" do not imply anything about past states, even though we'd usually expect a word like "closed" to, because of the "-ed" at the end. Oct 5, 2016 at 14:27
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    @DewiMorgan: yes - there's a big difference between an "open letter" and an "opened letter" :)
    – psmears
    Oct 5, 2016 at 16:59

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