【１】常識という言葉を辞書を開いて調べると、「一般の人が持っている、また、持つべき知識・理解カ・判断力」といった解釈をしている。
　ただ、私個人の解釈を言うなら「社会生活を営むうえで、当然知っている、と予想される知識」となるかもしれない。【２】この「当然知っている、と予想される」というところがこの言葉の難しいところだ。つまり、個人個人の考え方や生きてきた環境が違えば、この「当然知っている、と予想される」内容も少なからず違ってきてしまうからだ。
　【３】私の父、京助は東北の岩手県出身、母は生粋の江戸っ子だった。この二人はしょっちゅう意見が衝突していたが、それは正月の雑煮は何を入れるか、といった大変ささいなことから始まっていた。【４】父は絶対鮭の子を入れなくては正月のめでたい気分は味わえない、と言い、母はお雑煮にそんな生ぐさいものを入れるなんて聞いたことがない、と反論する。
　つまり、父にとっては雑煮には鮭の子を入れる、ということが「常識」なのであり、母にとっては入れないことが「常識」なのである。【５】そしておたがいに自分の「常識」が正しいと思い込んでいる。相手も自分と同じ考え方をするはずだ、と予想し、それが外れると、「あの人は常識がない」という言い方をする。つまり「常識」とは大変個人的な考え方の尺度だ、と言えると思う。
　【６】「世間」という言葉がある。これを英語に訳すとＷＯＲＬＤ（ワールド）になるが、「世界」と「世間」はちょっと違う。「社会」とも似ているが、受ける感じはやはり違う。土居健郎氏の『甘えの構造』によると、日本人の生活は一番内側に身内の世界があり、これは遠慮がいらない。【７】その外側に世間があり、そこでは窮屈な心遣いをすべきである。そしてその外側にまったく遠慮のいらない他人の世界があると考えられてきたのだそうだ。
　日本人にとって「常識」が大切になるのは、この「世間」の世界である。【８】ここでは身内の世界で学んだ「常識」がいろいろな形で試されることになる。「世間さまに笑われる」とか、「世間に出て∵恥をかく」というような言葉はいかにも日本的だ。
　しかしこの「世間」から抜け出して、まったく他人の世界に行ってしまえば、「常識」はそれほど大切ではないという考えになってしまうようだ。【９】日本人は公徳心がないとよく言われる。公園や道路に空きカンを投げ捨てたりするのは、この辺に原因がありそうだ。「旅の恥はかきすて」などとも言う。誰も知っている人がいなければ、何をしてもいいというわけであろう。
　【０】欧米にも我々のような社会生活を営むうえでの「常識」というのは当然ある。そしてそれは日本人の「常識」としばしば食い違うのもおもしろい。たとえば、私があるアメリカ人に大変世話になって、その次にその人の妹に会った。彼にはとても世話になったのでよろしく伝えてください、と頼んだ。日本人なら至極あたり前のことだ。ところがその妹はつっけんどんに、私と兄とは別々の人間で関係ない。そのようなことを頼まれるのは迷惑なことだ、と言うのでびっくりした。アメリカ人にとってはそんなことを言われるのは、常識外れということらしい。私はつくづく難しいものだと思った。
「郷に入れば郷に従え」という。つまり、「常識」というのは、そのくらい地域や家庭によって違う、ということだ。逆に言えば「常識」とは、必ずしも普遍的な知識ではなく、また合理的ですぐれたルールというわけでもないのである。

（金田一春彦「日本語を反省してみませんか」より）

Many of us like to keep pets. Why do we like them? Perhaps because they depend on us, or because they give us love. But what do we do for them? Watching tropical fish or stroking a cat are pleasant things to do and they can help to relax us if we are tired. But is it all right to keep animals as pets? Yes, if we take care of them well. But some pet owners do not. In cities many dogs are given too much food and not enough exercise.
The pet dog is often called“man's best friend". In old days dogs and humans took care of each other's lives. They protected people against enemies, like animals and other humans. They also hunted down food for their owners. Now we have shops, so we don't need dogs in the same way.
How kind are you to your pets? When you keep a pet, it needs a lot of care and attention. Hamsters are easier to keep than most pets. But they need enough space. Many pets feel pain in very small cages or because of bad care. Pets are not toys to be given as presents. They need regular feeding and care for many years.
Thousands of dogs and cats are abandoned each year because they are not wanted as pets any longer. Then they have to be destroyed by the police or animal welfare organizations.
Sometimes a pet has to be left with other people. The person taking care of your pet must always take care of it well.
Getting close to wild animals in a zoo is fun. We can learn a lot from animals. Small animals, like rabbits, can have all the space they need and are easy to keep. However, large animals, like elephants, become bored in a small space. Some of them need friends and a lot of space, but they sometimes cannot get them in a zoo.
Many wild animals have already died out because of human activity and many more are in danger. To keep living, they need to be alone in wild places. We need to try to balance our needs with wild animals' need. Zoos can help to save animals in danger. Good zoos can teach people how animals live in their natural homes, and how important it is to preserve the places they live in. This can help animals to live in the wild. Zoos can also help animals which have nearly died out. They can raise animals in zoos and then put them back in the wild.
Some wild animals, like elephants, need special protection because they are killed for their tusks. These are used as ornaments. All over the world wild birds and animals are in trouble because the places they live in are used by humans and they have no place to live in. Also we pollute the rivers and the seas. This damages and kills fish and the sea mammals that eat them.
Some people like to wear animal fur because they think it looks beautiful. In old days people wore animal fur because it was the only material they could get to keep warm. Today warm clothes made from plants or man-made materials, like polyester or nylon. But animals are still killed to make fur coats. Foxes, beavers, minks and wild cats are caught and shot.
People have eaten meat for thousands of years. Until recently animals were raised on small farms. Their owners knew that if they took care of them better, the food would be better. Today most meat is "factory farmed" -- the largest number of animals are raised in the smallest possible space. This means everyone in cities can eat cheap meat, milk and eggs. Not everyone agrees that we should eat meat, though.
Animals are used by scientists to examine how bodies work and sometimes to make new medicines. If scientists don't test new medicines on animals, people may lose their lives or health. Some people say we shouldn't use animals to do things we don't want to do. But do animals feel the same way as we do? Animals can feel pain, but many people think they cannot feel so much pain as we do.
People have used animals for fun for thousands of years. They have stopped some cruel sports, like dog fighting. But animals are still hunted for fun. People pay money to shoot lions in Africa. Sometimes the numbers of one animal in an area become too large for its own survival and that of other animals. So hunters say that they are not damaging animals by killing some. Many people think this is cruel.
Our relationship with animals is changing. We need them less for protection and food gathering. But we want them more for other reasons, like giving enough meat to many city people, trying out medicines and making lonely people happy. People damage animals when they put human needs before animal needs. Animals, plants and humans all live in the same world and depend on each other. So we must respect animals' needs like our own needs.