As most of you studying Japanese probably know, the language has to types of adjectives: Na-adjectives (i.e. 素敵(な)）and I-adjectives (i.e. 大きい). Each of these has different rules for conjugation into various forms.
There is a few words in Japanese that look like Na-adjectives that derived from a I-adjective. Here is a list of a few commons ones:
- 大きな （Similar to 大きい）
- 小さな (Similar to 小さい）
- おかしな（Similar to おかしい）
Even the way they are used (for example “大きな車”) is similar to Na-adjectives, but strictly speaking they are not.
The reason this matters in practice is because their usage is limited to the above pattern, and you would typically not use them in other forms as a true Na-adjective could be. Here are a few examples to illustrate this point.
- 大きな人 Correct
- 大きだ Incorrect
- 大きじゃない人 Incorrect
- 大きくない人 Correct
I found a very interesting post in Japanese which discuss this in detail here. The Japanese is somewhat difficult, but the quick summary is that you should treat these words a you would その and この. In grammatical lingo they are called classified as 連体詞 (pre-noun adjectival).