Here I have an explanation on the difference between zero conditional and second conditional:

enter image description here

I can't grasp the difference between to examples above:

This one is given as the example of zero conditional:

"You should see a doctor if a headache doesn't go away."

And this one is given as an example of first conditional:

"If your eyes hurt, you should check whether you need glasses."

The explanation says that zero conditional sentences describe situations that are generally or always true, and the second conditional sentences describe future possible situations. But it looks to me that each one of those two sentences matches both categories.

The book is "Perspectives", level 2.

  • 1
    You have written "second conditional" in the title. You must also cite the source, what is the name of the text book. You seem to have skipped other modals or an imperative can replace "will" The word "should" is a modal.
    – Mari-Lou A
    Commented Feb 29 at 11:44
  • @Mari-LouA - "You have written "second conditional" in the title" - Thanks. I'll edit the title. "You must also cite the source" - Why? How would that help?
    – brilliant
    Commented Feb 29 at 11:46
  • 4
    "You should see a doctor if a headache doesn't go away" is a universally true statement, while "If your eyes hurt, you should check whether you need glasses" maybe only applies in a particular situation or for a particular person (it may be specific "you"=the person being talked to, not generic "you"). I agree the difference is not very clear and they're not great examples. But anyone can post English lessons online and the quality is often not great.
    – Stuart F
    Commented Feb 29 at 11:50
  • Sources are important because we can tell you if they are reliable or not, and when quoting (just a reminder images cannot be searched) someone or something it must be attributed.
    – Mari-Lou A
    Commented Feb 29 at 13:33
  • 1
    @Mari-LouA - Okay. Just took it down. But how would people then know which "Perspectives" textbook exactly it is?
    – brilliant
    Commented Feb 29 at 14:40

1 Answer 1


It comes down to what it says in the image you posted:

  • Zero conditional sentences are situations that are generally true.
  • First conditional sentences describe possible future situations.

As is often the case, context matters.

Take the example:

"If your eyes hurt, you should check whether you need glasses."

If you saw this on a billboard, or someone randomly said it to you without knowing anything about your ocular health, then it would be a piece of general advice and an example of zero conditional. It meets the criteria - "you should" is an imperative with a modal. 'You' is the generic you', a colloquial substitute for 'one', so this is a piece of general advice that could apply to anybody.

However, if someone has just told you that their eyes hurt and you say this to them then it would be first conditional. You're not telling them a general piece of advice - you're giving them specific advice about what should happen in immediate future. 'You' actually means you.

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