Thomas Jeffreys, linguistic at large :-), says:

[Re Japanese borrowings form Chinese]I know. It doesn't count.
The majority of the lexicon of any language is
very fluid. Languages can (and do) borrow like crazy. The majority of
English words are derived from French and Latin, but that doesn't make
English a Romance language.

But aren't English and Romance words still cognates of each other if they
share the same root?  E.g. celestial/caelonis (or whatever; it's a long
time since I did Latin, and I don't get much practive :-) ).

The original assertion was that English IS NOT a Romance language, no
matter how many cognates it shares with French and Latin, and that Japanese
IS NOT a Sino-Tibetian language for the same reason. What determines
familial relation is the core lexicon and grammar, and in those respects
English and the Romance languages are dissimilar. As are Japanese and
Sino-Tibetian languages.

If two words truly derive from the same root, by either ancestoral relation
or borrowing, they are cognates. However, Japanese and Spanish have had no
significant contact (unlike Chinese), so you wouldn't expect very many
cognates in the first place, ne? Remember, a false cognate is a pair of
words that have a reasonable chance of being related, but are not. Thus,
it's an almost sure bet that "baka" and "vaca" are nowhere close in
meaning, and thus is not a false (or true) cognate.

(of course, in linguistics, a cognate is more precisely defined as a word
similar in sound and meaning, where false cognates do not have the same
root, and true cognates do)

I know that when I compared notes with someone who was learning Chinese,
we found that a lot of Japanese words are pronounced essentially the
same as their Japanese counterparts.  Wouldn't these be cognates?

Those would be (and are) cognates. Japanese and Chinese have a lot of true
cognates, and are likely to have a bitchload of false cognates, too. The
point was that Spanish and Japanese wouldn't share false cognates, because
it's far more likely to be a cognate of Chinese than of Spanish.

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