夜（よる）の海（うみ）は静（しず）かだ。 夜（よる）の海（うみ）は静（しず）かです。

さいきさんは親切（しんせつ）だ。 さいきさんは親切（しんせつ）です。

彼（かれ）は静（しず）かだ。 彼（かれ）は静（しず）かです。

私（わたし）は暇（ひま）だ。 私（わたし）は暇（ひま）です。

海（うみ）が綺麗（きれい）だ。 海（うみ）が綺麗（きれい）です。

それは便利（べんり）だ。 それは便利（べんり）です。

子供（こども）たちは元気（げんき）だ。 子供（こども）たちは元気（げんき）です。

今日（きょう）、レストランは賑（にぎ）やかだ。 今日（きょう）、レストランは賑（にぎ）やかです。

りゅうじの部屋（へや）は綺麗（きれい）だ。 りゅうじの部屋（へや）は綺麗（きれい）です。

今（いま）、暇（ひま）か。 今（いま）、暇（ひま）ですか。

これは簡単（かんたん）だ。 これは簡単（かんたん）です。

それは大変（たいへん）だ。 それは大変（たいへん）です。

<div class='writeup-body'>A predicate is a word that describes the topic/subject of a sentence. The Japanese equivalent of this is a 述語（じゅつご）, which literally means 'statement word'. As a predicate, な-Adjectives can appear by themselves (when the word they are describing does not need to be stated), or they may be used at the end of a sentence. It is important to remember that all な-Adjectives can also function as nouns, and therefore tend to sound more like a noun than an adjective, when used as a predicate.<ul class='writeup-examples--holder'> <li class='writeup-example'><div class='writeup-example--japanese'>素敵（すてき）。</div><div class='writeup-example--english'>It's wonderful.</div></li> <li class='writeup-example'><div class='writeup-example--japanese'>彼氏（かれし）は素敵（すてき）です。</div><div class='writeup-example--english'>My boyfriend is lovely.</div></li></ul>When there are no other words apart from the adjective itself, it comes across similarly to 'It's pretty', or 'It's hated', and similar expressions in English. We just have to guess what the 'it' is from context.<div class='writeup-caution'><div class='caution-header'>Caution</div>Unlike い-Adjectives, な-Adjectives change form depending on where they are in the sentence. At the end of a sentence, they will always be followed by だ, or です (except in casual conversation where だ is omitted). However, when used before the word they are describing, they will always be followed by な. Hence the name な-Adjectives.</div>In many sentences, either は or が could be used to mark the word/words that the predicate is describing. Which one sounds more natural will depend on many factors. In general, if you are specifically pointing out something as being different from other things in the same category, が will be used.<ul class='writeup-examples--holder'><li class='writeup-example'><div class='writeup-example--japanese'>有名（ゆうめい）な駅（えき）は汚（きたな）いです。</div><div class='writeup-example--english'>Popular stations are dirty. (In general)</div></li><li class='writeup-example'><div class='writeup-example--japanese'>この有名（ゆうめい）な駅（えき）が汚（きたな）いです。</div><div class='writeup-example--english'>This popular station is dirty. (Compared to other popular stations)</div></li></ul>In this example, が is distinguishing a specific station as having a unique level of dirtiness compared to others. は would sound unnatural in this type of sentence.<div class='writeup-funfact'><div class='funfact-header'>Fun Fact</div>Most な-Adjectives are words of foreign (Chinese/English) origin.</div></div>

Grammar Info

な-Adjective + だ (Predicate)

な-Adjective (Predicate)