I was browsing a famous social media website when I stumbled upon a post where someone was talking about how math teachers often speak and it mentioned some grammatical constructs which I often use in casual speech: "such that" and "thus".

English not being my native language (I'm French), I learned these from movies and online content mostly so I can't really tell if they are still "used" in day-to-day conversations.

I use "thus" a lot as a translation for "donc" to mean "implies", as in "The sky is blue, thus it is not red." I don't really know of any other word except for "so", but I often end up repeating it a lot so I replace it with "thus" sometimes.

"Such that" also seems familiar to me, its translation "tel que" being quite common in French.

  • I wouldn't say either are "old-fashioned" (they're certainly not like, say, hence, whence or thereby, whereby). It's just that in casual contexts today, it's usually much easier / quicker / more "natural" to just use so. Mar 27, 2019 at 19:03
  • FWIW, when I read the title of your question, I immediately thought of math class.
    – J.R.
    Mar 27, 2019 at 20:30
  • tel que is also such as. "thus" is used a lot in formal writing. I do French to English for a living but would never do the other way round even though I am also an interpreter. So and thus are not the same register necessarily. And are not always interchangeable. [by the way: that "those" should be "these"]
    – Lambie
    Mar 27, 2019 at 20:49
  • They may be old-fashioned, but the point is they are precise. Jun 8, 2020 at 11:19

2 Answers 2


Not really old fashioned, but fairly formal. People chatting casually don't usually say "thus", but it is common enough in (for example) mathematical writing.

It is not bad to vary your vocabulary, and you can often use "thus", "therefore", "which means", "implies", or reverse the order and use "if" instead of "so".

  • Right, casual chatters are not wont to use "thus". +1
    – Lambie
    Mar 27, 2019 at 20:50
  • 1
    Nor are they wont to use the word "wont"!
    – James K
    Mar 27, 2019 at 20:58
  • You got that right. :)
    – Lambie
    Mar 27, 2019 at 20:59

These are not old-fashioned, but they are not colloquial. They are mostly used in relatively formal writing or speech, though the fact that people with certain sorts of education - the sort that some would describe as making someone "more educated" - are more experienced with that sort of language means that such people will be more likely to use them casually.

Personally, I find such that a very convenient couple of words that saves me using more words to say the same thing with adequate precision. However, sometimes so that will do just as well, and that's what most people would say in everyday speech.

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