Why is it "were" and not "was"? I thought days are singular?

"was" is technically also correct. Standard English accepts both "was" and "were" for subjunctive.

Something something subjunctive mood

subjunctive

Been homeschooling my 1st grade son for 2 years now, and I just wanna say getting into the basics of English has opened my eyes to just how complex it really can be. Context and vowel placement are so touchy! He was spelling the word "one" and goes " W.... O..." and I said "man I hate to tell you youre wrong because youre on the right track but in THIS particular circumstance it starts with O" He was like "wait what?" He went to read the word "Me" and he sounds it out as "meh... eh..." and once again I have to go "You're on the right track sounding it out but in THIS case the E just sounds like the letter name" I was thinking, oh you think this is crazy wait until you find out how phone is spelled haha At this point I'm not sure how I ever learned to read as well as I can now with all these rules. I guess you get a foundation and then it's all just exposure and correction. Anyway I know that's off topic from the question but just wanted to share my experience.

Officially “were” is being used for the subjunctive, but the subjunctive in English isn’t so defined and most people would just use the normal indicative.

Subjunctive present tense. Using "was" here isn't grammatically correct but native speakers sometimes do it anyway. It's kind of a dialect thing.

you should try coming to suffolk. i can’t remember the last time i said was

"were" and "was" are interchangeable here .. Similarly in "If I were/was you, I would .." It's pretty common to hear both, at least in the UK. This sort of interchangeability is a bit of a minefield though when looking at colloquial speech and regional variations in my country (UK).

As previously explained, "were" replaces "was" in subjunctives and the second conditional. HOWEVER, this is an obsolete rule only fiercely enforced by grammar purists. The modern contemporary grammar absolutely accepts both forms as correct, and this should therefore not be treated as a mistake (as is often the case, unfortunately). It should also be noted that in formal writing it is always better to stick with "were".

If the phrase starts with “if,” it’s almost always “were”

This type of grammar is very formal and old-fashioned. You can forget about it. In real life, people say “I wish that today was Friday”.

Research the subjunctive. It’s just some separate conjugations that we use for some verbs if the sentence is a wish/command/hypothetical situation ect. We don’t have as many different conjugations for it as other languages so it won’t be too difficult to learn though it will still be a pain.

It's the subjunctive mood, which is sort of dying in English but is still around for now!

Uni-educated Scot. I never used the subjunctive, never really considered it more than an archaic or posh mode of speech. I seem to come across this particular usage more these days than before...odd.

I'm over 30 and been speaking English my entire life. This page has taught me more than I care to admit. I would say "was" here as well ...

Subjunctive is kinda weird in English, sorry, pal

I'm a native English speaker, and if you said "was," I wouldn't correct you. It sounds right to me.

It's the same as "if I were you...." subjunctive pattern

was works too in casual speaking, no one will notice

On a related note OP, the sentence in your post title should be "I thought days WERE singular" instead of "I thought days ARE singular".

I don’t remember learning about this in school, although I think this sub for actually giving it a name haha. I actually knew about this because of a song from Beyonce ‘If I were a boy’

Don’t feel bad. Many many many folks will use “was” in this instance, and while it’s not necessarily correct, few will even catch it.

Was is less formal

Its technically correct in the most formal English to use were here but I don't meet very many people who know that much less use it

It's in the subjunctive mood, lucky for you the subjunctive isn't that hard to learn in English

This is the subjunctive. In American English, at least, it's gone out of fashion. Most Americans would say "was". I don't know if that's the case in other regions.

It’s subjunctive tense. It’s similar to how you say “if I were you” rather than “if I was you”. You kinda have to learn it on a case by case basis when to use subjunctive tense and when not to

For the purposes of using English in conversation, "was" is fine.

Subjunctive. "Was" is also common among native speakers. The subjunctive mood for verbs in english is slowly dying.

Again, it's the subjunctive, but I can assure you that many native speakers say was as well...

I am by no means an expert on grammar even as a native English speaker. “Were” versus “was” is just depending on situation in my opinion. “Were” is more formal and sounds better, but I have heard people use “was” before and nobody would question it. Here is an example: I wish it were Christmas still. I wish it was Christmas still. Both sound good, nobody would question you for using either.

We use "were" for imaginary scenarios.

im a native english speaker and im 16, i have never heard anyone speak like this, to me, this looks extremely formal and unnecessary. maybe dont take advice from me, but if you say 'was' i dont think anyone would care

Past subjunctive. It is more formally correct to use "were" when referring to unreal situations, although it is still very common to use "was".

If you know the grammar structure for the conditionals, you will that the second conditional that always has a past simple as the first part, has the special rule where you can use were for all the subjects no matter if they are third person or not. The verb wish is formed very similarly so when you use it to express a present wish, you can use were for all the subjects.

Subjunctive mood

It's the subjunctive tense. Other European languages have this too.

It’s the subjunctive, you use “were” instead of “was” with imaginary scenarios that begin with “I wish”, “if”, etc. I wish I WERE better at sports. If I WERE more qualified, I may have gotten the job.