Are foreign adjectives always な adjectives?

Question

Sitting in a restaurant yesterday I saw a sign advertising a mango flavoured bagel. It was described as トロピカルな味.

That just got me wondering... whenever a 外来語【がいらいご】(word taken from a foreign language / "loan word") is used as an adjective, is it always a な adjective?

Are there any examples of loanword い adjectives?

Are there any general guidelines as to how loan words are made to conform to Japanese adjective rules.

(Please note I'm not familiar with linguistics, so even though I'm asking a fairly technical grammatical question, please dumb it down for me as much as possible. Thanks!)

Answer 1

If you're OK with エロい　(as discussed in comments), there are examples like:

• エロい
• グロい
• ナウい

But note that these are directly derived from エロ(チシズム), グロ(テスク), and ナウ　("now"). They were not borrowed into the language as -i adjectives; they were borrowed into the language as nouns and/or na adjectives, and then THOSE borrowings were turned into -i adjectives. Ultimately, this is a form of slang/language play along the lines of the verbs タクる for "take a taxi", マクる for "eat at McDonalds", etc.

So, to get back to the original question, yes. Foreign adjectives always start out as な adjectives. This is a clear rule in Japanese dating from the days of strong Chinese influence. Even when the borrowed word actually ends in an -i sound (e.g. ファジー, セクシー), it is still treated as a な adjective when it first arrives in Japanese. But, once they are in the language, they can be broken down and then reborn as -i adjectives, a la グロい.

The interesting issue, I think, is: how "real" are these 二世 -i adjectives? On one end of the scale, I think that エロい and グロい are completely unremarkable now in colloquial Japanese. No-one thinks of them as wordplay. At the other end of the scale, I have heard things like セクシくない, but only as a joke. Treating セクシー is if it were セクシい, an -i adjective, even though both speaker and listener know that it is not, is unexpected and therefore amusing. Sort of like how in English we might say "You think that's amazing? I can show you something even amazinger!" even though we know that "amazing" doesn't take the "-er" ending.

(Tangent: Note that セクシい is structurally different from グロい: instead of taking the first two morae and making a new stem, it just reinterprets (intentionally misinterprets) the existing sounds of the word セクシー. This may be one reason why セクシい remains at gag level while グロい is already a regular word. Maybe the only way to create unremarkable adjectives/verbs from gairaigo in Japanese is to create a two-mora stem and build on that, and any other method will always remain at the humorous level. I haven't looked into this too deeply. It would be especially interesting to look at perceptions of these words among people born before and after they were created.)

Answer 2

Reading up on sound symbolism, I found this

Nasal consonants like n and m convey warmth, tactuality, softness, and sound more personal and subjective.

e.g. むちむち　(plump)

The な　in な-adjectives is a nasal sound. I conject that they are subjective descriptions.

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Also consider the comparison between adjectives ending in ~しい and those ending in ~い:

For ~しい type adjectives,

悲しい

寂しい

楽しい

These are adjectives that cannot be objectively measured, hence subjective. (And also a large majority of them describe psychological states)

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For ~い type adjectives,

重い

広い

暑い

These are objectively described; they can be measured.

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Conjecture:

For トロピカル　there is no objective scale for "tropical-ness" hence it takes on な. It does not take on ～しい since it is not a psychological　description (as most ～しい adjectives are).

For エロ my dictionary shows both エロな and エロい.

So depending on whether subjectivity/objectivity is conveyed, it corresponds to the use of な or　い.

See also "i-adjectives used as na-adjectives: is there a difference? (e.g. 大きい versus 大きな)"