Try this: https://www.lawlessfrench.com/grammar/cest-vs-il-est/

-- Chris.

I have read that, and the material on Kwiziq. I find myself still confused in this particular case.

Which one would you go for? And what would your thought process be?

I would say "Il est logique...". I have a hard time, however, justifying it or reasoning it out. It does, however, follow the rule Il+adjective versus C'est+noun noted in the link I sent you.

From your questions I get the impression that you are approaching learning French very methodically (which is good) and very rule-oriented (which is sometimes not so good). Have you tried just to assimilate a novel idea rather than dissecting it? It helped me a lot to read as much as I can and not stop at every phrase I wasn't entirely sure about. Just make a mental note and go on. In French there are probably more exceptions to any given rule than in any other language anyway :)

Greetings, -- Chris.

It is true that I can read and not bother about c'est vs il est, and if I finally get to write or speak to someone in French they can probably forgive my occasionally getting my grammar wrong. But just for now I have to answer these questions in Kwiziq and Duolingo and the standard is 100% perfection and to get there I need to learn and rember the logic.

I have achieved it too, with 100% in all 6 levels in Kwiziq and a golden tree in Duolingo, but then I get to things like the Kwiziq writing challenges and realize how little I know compared to even a 5 year old French child.

I suppose that if I could immerse myself in the culture these things would eventually come intuitively but since that cannot happen I have to make do with what I can achieve online.

---

I agree that the FrenchToday page, which simplifies everything to il est+adjective or c'est+noun, would give us "Il est logique...".

But the Kwiziq lesson we are discussing here says:

Case 1: C'est + noun

Case 2a: C'est + anything else, where we are making a general, unspecific statement or opinion about prementioned things.

Case 2b: Il est + anything else, where we are making a statement or opinion related to specific prementioned things.

For It is logical that you have gone first we do not have a noun so case 1 is out.

At first it sounds like we have case 2b - so Il est logique - since we have a specific thing, i.e. "you have gone first".

But then I look at one of the examples for case 2a and it says "It's really beautiful here" = "C'est vraiment magnifique ici" and I think it sounds just like out "It is logical..." statement, even though it is, to me, talking abut a specifc thing, namely "here".

But in both cases the "specificity of the thing" is kind of vague.

Unfortunately the examples for case 2b do not help because they are so simple. Each consists of two consecutive sentences. One that asks a question about a thing and another that makes a statement about it. The "It is logical that..." statement is unlike those.

So I lean toward case 2a and "C'est logique...".

This Kwiziq lesson is about giving opinions on things, I don't think it's relevant to your example. (The FrenchToday lesson doesn't cover this kind of sentence either in the main lesson, although it is mentioned in the comments below.) A closer match on Kwiziq would be this lesson:

Il est [adjectif] que + the subjunctive mood (Le Subjonctif) = It is [adjective] for [someone] to ... in French

You can see that they use "il est" exclusively here, which I think is appropriate for written French. Informally, I believe you could use "c'est" instead. 

Thank you for that. I think you have provided the answer I was looking for:

When using expressions for general opinion such as "It is important for <someone> to <do something>", in French you will use the structure Il est <adjective> que followed by Le Subjonctif.

Where opinon words include: important, nécessaire, inutile, esssentiel, logique, ...