past tense na adjective + noun

Question

I have two sentences that im using to try to understand how na adjectives are conjugated in Japanese.

1. 私の友達は綺麗な人 - My friend is a beautiful person
2. 私の友達は綺麗だった人 - My friend was a beautiful person

In Tae Kims guide to Japanese he gives the following patterns for conjugating Na adjectives:

|                   |    Positive       |      Negative         |
|:--------------:   |:--------------:   |:------------------:   |
| Present/Future    |   Na Adj + da     |   Na Adj + janai      |
|      Past         | Na Adj + datta    | Na Adj + janakatta    |

My question is this, if im using the past tense of 綺麗 to modify the noun 人 do I still need the な in between?

Most other guides I have read tell me to use the past tense of です after the modified noun in order to show past tense, something like this:

私の友達は綺麗な人でした。

Isn't this the polite form?

Im really confused about this. Can anyone provide some guidance on where im going wrong?

Answer 1

Part of the confusion appears to arise from the fact that your two "sentences" are actually incomplete.

1. 私の友達は綺麗な人
2. 私の友達は綺麗だった人

These are fragments: they are only phrases, not full sentences. They could end in the copula (だ for plain-form familiar speech, です for polite speech), or they could end in something completely different:

1. 私の友達は綺麗な人 [をかみ殺して食べる。] - My friend [bites to death and then eats] beautiful people.
2. 私の友達は綺麗だった人 [をかみ殺して食べる。] - My friend [bites to death and then eats] people who were beautiful.

Even with the copula, the meaning is slightly different for the second one:

1. 私の友達は綺麗な人 [だ・です] - My friend [is] a beautiful person.
2. 私の友達は綺麗だった人 [だ・です] - My friend [is] a person who was beautiful.

If a な adjective is in the past tense, the な is replaced with だった, and the meaning parses out to "was [ADJ], used to be [ADJ]".

If you just mean that the past tense should apply to the whole statement, you would use the past tense for the final copula, but leave the adjective in the regular attributive form (using the な):

• 私の友達は綺麗な人 [だった・でした] - My friend [was] a beautiful person.

Answer 2

Declinable word conjunctive form (連用形 in Japanese) for i-adjective and na-acective show their past tense pattern by adding た.

明るい　⇒　明るかった
重い　⇒　重かった
美しい　⇒　美しかった

穏やかな　⇒　穏やかだった
きれいな　⇒　きれいだった
上手な　⇒　上手だった

If you want to use them for modifying any noun, just put noun after them
明るい季節　⇒　明るかった季節
美しい人　⇒　美しかった人
穏やかな日々　⇒　穏やかだった日々
きれいな人　⇒　きれいだった人

Now we place adjectives at predicate position.
今が一年中で一番明るい。
先月が一年中で一番明るかった。
今が一年中で一番穏やかだ。
先月が一年中で一番穏やかだった。

If we add polite ending word;
今が一年中で一番明るいです。
先月が一年中で一番明るかったです。
今が一年中で一番穏やかです。
先月が一年中で一番穏やかだったです。

But ending word です also has past tense form. Because i-adjective + でした is still under polemical circumstance, I would like to avoid touching this matter now. For na-adjective, below patterns are possible.
先月が一年中で一番穏やかだったです。
先月が一年中で一番穏やかでした。

Also we try to make adjective modified noun at predicate position.
今が一年中で一番明るい季節です。
先月が一年中で一番明るい季節でした。
先月が一年中で一番明るかった季節です。
もう何週間も穏やかな毎日です。
あのころは穏やかな毎日でした。
私が覚えているのは穏やかだった毎日です。

Those are the ways how adjectives are made into past tense.