❶～である ⦣ is は主語が 3人称しょう単数の時の be の現在形.
This is my sister. Her name is Mary. She is ten.
♔基本This is my sister. Her name is Mary. She is ten.
これが私の妹です. 妹の名前はメアリーです. メアリーは10歳さいです.
⦣ 3人称単数の（代）名詞＋is＋名詞[形容詞].
Today is Sunday.
Today is Sunday.
きょうは日曜です.
The sky is blue.
The sky is blue.
空は青い（です）.
When he is sick, he will see a doctor.
When he is sick, he will see a doctor.
彼は病気になったら医者に行くでしょう.
⦣ When he is sick は未来のことを言っているが, このような副詞節では現在形を使う. ×When he will be sick としない.
Is that your bicycle?
♔基本Is that your bicycle?
あれは君の自転車ですか.
⦣ Is＋3人称単数の（代）名詞＋名詞[形容詞]?. That is your bicycle. （あれは君の自転車です）の疑問文.
This is not my bicycle.
♔基本This is not my bicycle.
これは私の自転車ではない.
⦣ 3人称単数の（代）名詞＋is not＋名詞[形容詞]. This is my bicycle. （これは私の自転車です）の否定文. is not は話し言葉ではしばしば isn't と縮められる.
What's (=What is) this? Is it a rope?—No! It isn't a rope. It's a snake!
会話What's What is this? Is it a rope?—No! It isn't a rope. It's a snake!
これは何だ. ロープかな.—違ちがう! ロープじゃない. それはヘビだよ!
It's (=It is) a lovely day, isn't it?
It's It is a lovely day, isn't it?
いいお天気ですね.
⦣ It は漠然ばくぜんと「天候」を表す. isn't it? は「ね」と念を押おす言い方. この場合 ×is not it? としない.
❷（～に）いる, あるthere ❷
He is in his room.
♔基本He is in his room.
彼は自分の部屋にいる.
⦣ 3人称単数の（代）名詞＋is＋場所を示す副詞（句）.
The cat is on the roof.
The cat is on the roof.
そのネコは屋根の上にいる.
The bag is under the table.
The bag is under the table.
そのかばんはテーブルの下にあります.
＊会話＊
Is your father at home?—No, he is not （at home）. He's He is at his office.
お父さんはご在宅ですか.—いいえ, （うちに）いません. 父は会社にいます.
Tom Hanks is in town.—Oh, is he?
会話Tom Hanks is in town.—Oh, is he?
トム・ハンクスが町に来てるよ.—へえ, そうなんだ.
⦣ あいづちを打つ用法. 