Sorry the topic might not make much sense. Anyway I Was doing lessons on lingodeer grammar and this came up.
Now I was under the impression that the word 大きい was one word but their explanation seem to imply that the い is a suffix. Same thing with 美味しい。And if I understand correctly they are both I adjectives. Was this the case of them generalising their I-adjectives or??
Sorry if my question doesn’t make any sense.
Yep, the い in い-adjectives is suffix! It can’t stand on its own or be attached to words that aren’t い-adjectives, though.
In this case, です is just added for politeness. い-adjective + だ is ungrammatical.
ETA: The stem 大き (おおき) can be conjugated like this:
大きい → non-past
大きくない → non-past negation
大きかった → past
大きくなかった → past negation
大きく → adverb ‘in a big way’
大きさ - noun form ‘size’/bigness
(add です to any of these for extra politeness)
But also … it can be conjugated like this (so can 小さ, but most adjectives can’t):
大きな(noun)
implied (but unused): 大きだ・です - non-past
implied (but unused): 大きじゃない - non-past negation
implied (but unused): 大きだった・でした - past
implied (but unused): 大きじゃなかった・じゃなかったです - past negation
You’ll notice that ない is also an い-adjective, and so is the -たい form of verbs.
Also, 大き can have other suffixes such as く or さ, such as 大きく成りました (became larger). Or 大きさ (size).
I would still consider 大きい the word. But as the others said, the stem is 大き, allowing 大きい to conjugate into 大きく, 大きくない, 大きさ, etc.
Thanks so much for your explanation. Makes so much sense now. I should probably study more in depth grammar.
Definitely!! 大き can’t stand on its own! The い is a bound morpheme.
Which is exactly what you’re doing. 
頑張って！！
