[asveikau]

See the section "historical dispute".

I think some people get touchy about them being lumped together if their last period of commonality (per the article) was 1400 BCE. For comparison, I believe all the Slavic languages were mutually intelligible around 1200 AD. But much more recently than this, in the last few centuries, there have been notable attempts by east slavs to absorb the Baltic language cultures and deny them.

[krzyk]

I doubt that South Slavic and West/East Slavic were mutually intelligible at 1200 AD.

I doubt West and East Slavic were. But inside those geographic groups they probably were (Czech and Polish AFAIR were around that time).

[asveikau]

I may be off by 100-200 years, but this is what I read. There were accents and regionalisms but they were all mutually intelligible.

It is an example I think of often, about how quickly languages can change. In the scale of 1000 years, a lot changes. Most of the diversity in Romance languages is from around that timescale too, it really started to diverge substantially around 900ad-1100ad.

[actionfromafar]

Depends on your standards, too. Even today, any pair of slavic speakers should have a head start in understanding each other. Put them next to each other for a month and they should be talking, at least about basic everyday things.

[krzyk]

Not quite. My anecdotal examples. I'm Polish.

I was in Crimea for about 2 weeks (in 2012) they split me Russian there. I couldn't understand a word they said. And I didn't learn to understand than for 2 weeks of travel there.

I could understand some words from Ukrainian (I traveled by train from Lviv).

Another example is Croatian, I've been there on vacation and renting a room. I couldn't understand a word they said and didn't learn any.

TlI can understand some Czech (because this is the closest language together with Slovakian to Polish) but that's it.

I wouldn't mix Slavs from different groups together. They evolved separately and are as close as English and German.