# 'a' versus 'one'

Should "a" or "one" be used in the below examples, and why?

An atomic reaction in a reactor causes atomic reactions in all the other reactors.

An atomic reaction in one reactor causes atomic reactions in all the other reactors.

A civil war in a country can spark wars in all the other countries.

A civil war in one country can spark wars in all the other countries.

• Quite a lot of the sentences aren't true. Commented Oct 26, 2022 at 15:02
• I know that the examples are quite meaningless but I could not come up with better ones. I would focus on the theoretical problem suggested rather than on the specific meaning of the provided sentences. If you have better example sentences please feel free to add them!
– user163195
Commented Oct 26, 2022 at 15:06
• "One" is correct grammar in all your examples.
– gotube
Commented Oct 26, 2022 at 15:56
• Rather than posting four examples, it would be better to post one or two and explain why this is unclear. You could explain why you think "a" or "one" is incorrect. You could explain if you think the meaning is the same, or if you think it is different (an how it is different). One example may be enough, or two for comparison. Commented Oct 26, 2022 at 19:19
• @gotube - Do you mean that using "a" is wrong?
– user163195
Commented Oct 27, 2022 at 6:28

Although the indefinite article 'a' does denote one of something, it is also non-specific.

You should use 'one' in your example, because it is one of a specific set of reactors in a specific plant.

"A reactor" could be any reactor, as if what you are saying applies to any and all reactors anywhere. That also confuses the scope of what you are trying to say - if any reactor has an effect on others, which others does it affect?

If there was only one reactor in the plant then you'd say 'the reactor'.

• Thank you. I have read a number of times your answer because I don't fully understand it.
– user163195
Commented Oct 26, 2022 at 15:18
• I have been pondering your answer. Let us see if I understand you well: 1) If I am talking about an unspecified reactor in any of the nuclear power plants in the world, I should use "a", 2) If I am talking about a specific nuclear power plant and no specific reactor of the plant, I should use "one", 3) If am talking about a specific nuclear power plant and a specific reactor in it, I should use "the". Right?
– user163195
Commented Oct 27, 2022 at 6:32
• @goalie If you mean one of a specific set, then use 'one'. Let's say there are 6 reactors in a nuclear power plant. If one (of that set) reacts, they all react. The problem with saying "a reactor" is that (i) it isn't specific to the power plant unless you specify, but even if you do specify, it may not make it clear that there are more reactors within that power plant. By saying "if one reactor in the plant explodes, they all explode" it conveys everything you would need to say - that there are multiple reactors in a plant, and any one affects the others. Commented Oct 27, 2022 at 10:28

If you use the form: "in all the other [things]", then you should use 'one'. This is because the 'the' means you are talking about a specific set of things and selecting one from them.

If you were to use the form: "in all [things]", then you can use 'a', because you are not talking about a specific set but every other [thing] in existence, although, 'one' is still correct.

• What would be the difference between "a" and "one" in the second case?
– user163195
Commented Oct 27, 2022 at 6:35