Suppose I am enumerating reasons not to fly. Is it then correct to write/say:
Firstly, I prefer the train because I can see the landscape. Secondly, I have control over my luggage, and thirdly, it is better for the environment.
Or is it:
First, I prefer the train because I can see the landscape. Second, I have control over my luggage, and third, it is better for the environment.
I thought the first should be correct, but I find the second one in written texts. Which one is correct?
Both styles are used. In most genres, no-one will object to either. However, traditionally, first, secondly, thirdly etc. is used. Only pedants will insist on this usage, but it is something to be aware of, as there are many pedants. See Fowler's Modern English Usage (3rd edition).
The Oxford English Dictionary on firstly:
Used only in enumerating heads, topics, etc. in discourse; and many writers prefer first, even though closely followed by secondly, thirdly, etc.
Burchfield in Fowler's Modern English Usage on first:
First, and firstly are both correct, since first is also an adverb. So you can say:
I prefer the train because I can see the landscape. Secondly, I have control over my luggage, and thirdly, it is better for the environment.
First, I prefer the train because I can see the landscape. Second, I have control over my luggage, and third, it is better for the environment.
The important thing is not to mix them, as in the following sentence:
First, I prefer the train because I can see the landscape. Secondly, I have control over my luggage.
This answer at ELU suggests:
Both are correct, however, there is "overcorrectness" in using firstly because it seems more like an adverb than first.
Go on the length principle: both have the same meaning, but firstly is two characters longer than first. The language will eventually evolve to do without the longer equivalent; I'd use first.
From Cambridge website, mentioned:
We often use first, especially in writing, to show the order of the points we want to make. When we are making lists, we can use first or firstly. Firstly is more formal than first
So, If you are doing academic writing use Firstly, otherwise, use First for general writing use.
From this ELU post first answer, it is said that:
Eric Partridge ("Usage and Abusage") says:
firstly is traditionally said to be inferior to first, even when secondly, thirdly ... follow it.
As many others have mentioned, both are perfectly fine. Additionally "firstly" is more formal than "first" to most. Another ELL answer on that can be found on it (add on @Dongrui_Yang's answer).
Some alternatives are found here:
firstly = first off / "for a start..."
secondly = next / and then / another thing
moreover/furthermore = on top of that/this
It is said by Grammarist that:
“Firstly,” “secondly,” and “thirdly” are superfluous terms. “First,” “second,” and “third” are more acceptable words for enumerating text in writing. Experts also prefer “first” even if the other items state “secondly” and “thirdly.”
It is also said from Merriam-Webster that:
In writing, first is much more common than firstly and is probably the best bet for most situations, even if the only reason is that a reader may wonder if firstly is proper and be distracted by this word choice.
If you are writing as a list (which most intend), use first, second and third. After all, if reading as a list of prioritised numbers, say, you wouldn't retort 'onely'; it would be 'one', 'two' and so on. Hence first, second etc. No need for the ly. This 'error' of 'firstly' etc is almost annoying as the improper use of 'which' (without punctuation), when most should actually be using 'that'.....
