I hope you guys don't mind me posting all my random Japanese language questions here!
okay
Tae Kim's Guide says..
(1) 高いビル。- Tall building.
(2) 高くないビル。- Not tall building.
(3) 高かったビル。- Building that was tall.
(4) 高くなかったビル。- Building that was not tall.
Now, this makes sense but my textbook contradicts it.
Textbook (EASY JAPANESE 'A Guide to Spoken and Written Japanese, Jack Seward):
"The past tense positive of all A (-i) adjectives is easily formed by dropping the final i and substituting katta. Thus, the past tense of
chiisai (small) becomes
chiisakatta. However, this past positive form can only be used as a verb," (at the end of the sentence) "e.g.,
Sono hako wa chiisakatta (That box was small). We cannot say
chiisakatta hako for a 'box that was small'"
Which is correct? Is jack saying that only to steer readers away from unnatural speech? :?

ありがとう
Whmm, interesting. The following is just my opinion.
There's another classification of adjectives according to the meaning; 属性形容詞(attributive adjectives) and 感情・感覚形容詞(emotional/sensuous adjectives).
Attributive adjectives are used in the present tense to express the thing unchanged by time.
海は広い。
The sea is wide.
地球は青い。
The earth is blue.
GENERALLY, 小さい箱(the small box) is always small regardless of the passing of the time. Therefore the expression 小さかった箱(the box that was small) strongly suggests the "change" of the box, as undrentide explained.
小さかった箱がなぜか大きくなっている。
For whatever reason, the box that was small becomes big.
On the other hand, emotional/sensuous adjectives can be used in the past tense more easily, because emotion/sense is basically temporary.
痛かった足を引きずって歩いた。
I dragged my sore foot. (I dragged my foot that was sore.)
This 痛かった is simple past, does not imply the "change". On the same time the writer/speaker dragged his/her foot, the foot was sore. So you can also say 痛い足を引きずって歩いた. There is basically no difference between the two sentences.
As for the adjective 小さい in the expression サイズが小さかったその帽子 in ASHIKAGA's example, it's rather close to the sensuous adjective; something like サイズが小さいと
感じた帽子. The sense that he felt when he put on the hat is already past. So the phrase 小さかった帽子 can be used here. And 小さい帽子 also can be used because the hat was still small at the time it hurt his scalp.
サイズが小さかったその帽子は、彼の頭皮を痛めたので
サイズが/の小さいその帽子は、彼の頭皮を痛めたので
Probably these sentences have the same meaning.
Futhermore, the textbook may try to explain "the tense issue".
小さい木がある。
There is a small tree.
(There is a tree that is small.)
小さい木があった。
There was a small tree.
(There was a tree that was small.)
小さかった木が大きくなっている。
The tree that was small is grown (now).
小さかった木が大きくなっていた。
The tree that had been small was grown (then).
Anyway, as ASHIKAGA wrote, Jack Seward's statement is too much rough, in my opinion.