ものだhow things are; should; used to
ものだ stands back and says how things are. That gives a general truth and a common-sense "should". With feeling in it, it marvels at something or looks back on the old days.
how things are
In a place you aren't used to, anyone is nervous at first.
used to
In my student days, my friends and I would talk for hours in a coffee shop after class.
How to form it
Plain form of a verb or adjective + ものだ
A な-adjective keeps な: 複雑なものだ. Polite ものです, written ものである. In conversation it shrinks to もんだ.
Should not
Verb in the dictionary form + ものではない
The verb is something a person chooses to do. In conversation もんじゃない.
Which ものだ is it?
What comes before it usually tells you.
A plain present form about people or things in general
That's how things are.
People change.
A dictionary-form verb for something a person chooses to do
That's what people do, so do it: "should".
You're supposed to let people finish what they are saying.
The same, with ものではない
That isn't done: "shouldn't".
You don't say things like that.
One thing you have noticed, often with な or ね after it
Wonder, or a sigh: "how …!"
How time flies.
A た-form about one thing that happened, often with よく or ずいぶん
Wonder again: よく is "I'm amazed that…".
I'm amazed you made it all the way here without even a map.
A た-form with a time long gone: 昔は, 子どものころ
Looking back: "used to", and よく is "often".
When I was a child, I used to swim in this river a lot.
How things are
About people, life or things in general, never one event. English uses the plain present, or adds "naturally" or "tend to".
Any job takes time to get used to.
Everyone gets things wrong at first.
Often said to cheer someone up: it happens to everyone.
After something that just happens, ものではない is this use in the negative, not "shouldn't".
Plans don't always go according to schedule.
Should and shouldn't
With something a person chooses to do, "that's how people behave" means "so behave that way". It is a parent, a teacher or an older person putting someone right about manners. To a friend it sounds like a lecture, and it isn't said to someone above you.
You're supposed to give up your seat to old people.
You don't treat borrowed things roughly.
You don't play with your food.
もんじゃない, as it is said at home.
ものだ or べきだ?
You don't laugh at other people's mistakes.
It isn't done. You point to how people behave.
You shouldn't laugh at other people's mistakes.
It is wrong. You give your own judgment of what is right.
ものだ is a rule for everyone, even when it is said to one person. What this person should do this time is べきだ: 君はすぐ謝るべきだ, "you should apologize right away", not 謝るものだ. Advice for this one case is ことだ, or from a friend たほうがいい.
Being struck by something
One thing makes you stop and marvel, or sigh. English has only "really", "how …" or a tone of voice. Two set phrases: 早いものだ, "how time flies", and たいしたものだ, "that's really something".
That tiny little kid, in college already. How time flies.
To get this good in only three months, that's really something.
I'm amazed you solved such a complicated problem in one night.
よく with a た-form: amazement that someone managed it.
Looking back: たものだ
After a た-form, ものだ is never a general truth or a "should". With a time long gone, it recalls what you did again and again, or how things were, usually fondly.
Every winter, my grandmother would toast rice cakes on the stove for us each morning.
This street has changed a lot, hasn't it?
Yeah. We used to play here a lot after school.
English "used to" can be a bare fact: "I used to work at a bank." たものだ always has feeling in it, so a bare fact is just the past: 前は銀行で働いていた.
When もの is something else
もの is also the everyday word for "thing".
This watch is one my father gave me.
Not "used to". もの is the watch.
With more before or after it, it is a different form.
With から or で after it, a reason: the "because" of apologies.
The traffic was terrible, so I ended up being late for the meeting.
たいものだN2
After たい, a wish said with feeling: "I'd love to".
Just once, I'd love to see the northern lights.
というものだN2
After という, a verdict: "that is what … means".
Helping each other when things are hard: that is what friendship is.
ものがあるN2
With がある: "there is something … about it".
There is something about her singing that moves people.
Check yourself
1What does this mean?
一人で
Choose an answer to see why.
2A friend has upset Tanaka and asks what you think. Which do you say?
Choose an answer to see why.
3A mother says this at the table. What does she mean?
ご飯を
Choose an answer to see why.
More detail
With よくも, the amazement is anger: "how dare you".
How dare you say such an awful thing.
More sentences
As you gain experience, the way you see things changes too.
People's feelings are complicated.
You don't pretend not to see someone who is in trouble.
Compared with ten years ago, this town really has changed.
Not "used to": the town has changed, and you are struck by how much.
When I was in high school, I would study until the library closed whenever exams were coming up.
There used to be rice fields all around here too.
To have achieved this much in so short a time is truly remarkable.
ものである, as formal writing has it.