さえ・
On its own さえ is "even": the extreme case, the last one you'd expect. With a ば-form after it, it is "as long as" or "if only": that one thing is all it takes.
even
He was so nervous that he couldn't even say his own name.
as long as
As long as I know the address, I can find it on the map.
Even
Noun + さえ
It usually takes the place of が and を. Other particles stay, in front of it: にさえ, からさえ. For the one who does something, でさえ is common too, with the same meaning: 子どもでさえ.
As long as: a noun
Noun + さえ + ば-form
お金さえあれば, 天気さえよければ.
As long as: a verb
ます-stem + さえすれば
読みます → 読みさえすれば.
As long as: something that goes on
て-form + さえいれば
練習してさえいれば.
Which one is it?
What follows さえ tells you. A ば-form (あれば, すれば, いれば), or たら or なら, nearly always means "as long as". Anything else is "even".
Even
What comes before さえ is the extreme case: the easiest thing, the smallest amount, the last person you'd expect. If it is so for that, it is so for everything else. With a negative, it is "not even".
Even a primary-school child can solve this problem, and yet I, an adult, got it wrong.
Even Tanaka, who is normally so calm, was against that decision.
There wasn't even a hundred yen left in my wallet.
He hasn't told even his family about it.
に stays, and さえ follows it.
さえ, も, でも or まで?
My throat hurts so much that I can't even drink water.
Everyday speech. On the least thing, with a negative, plain も is already "not even".
My throat hurts so much that I can't even drink water.
The same with more weight. さえ is a step more written.
でもN4
After a noun, the everyday "even": 子どもでも分かる. でさえ says the same with more weight.
Even a beginner can take part in this course.
までN4
"Even" from the other end: the surprise on top of what was already there. "Not even" is usually さえ or も.
It's cold today, and now it has even started to rain.
As long as, if only
One condition is all it takes: with that, the rest follows.
As long as I have time, I'll go.
Time is the only thing in the way.
Even if I don't have time, I'll go.
"Even if" is ても, not さえ.
If you just read the instructions, setting it up is easy.
As long as you keep practicing a little every day, you are sure to get better.
If it's all right with you, Ms. Tanaka, shall we go together?
After a name, 〜さえよければ is a polite "if it's all right with you".
If only I had the money, I could study abroad.
With のに at the end it is a wish: the one thing is missing.
Close neighbours
すらN1
The same "even", mostly in writing. It has no "as long as" use.
I was so busy that day that I didn't even have time for a drink of water.
こそN3
こそ marks the one that counts, not the extreme case.
Today I really am going to finish the report.
Check yourself
1What does this mean?
パスポートさえ
Choose an answer to see why.
2What does this tell you?
この
Choose an answer to see why.
3Which one fits?
使い方を
Choose an answer to see why.
More detail
さえも is the same さえ, a little stronger. A whole action takes こと first.
Even the experts couldn't predict that change.
He was so busy that he even forgot to eat lunch.
ただでさえ is a set phrase: "as it is", before something makes it worse.
I'm busy enough as it is, and now I've got even more work.
たら and なら can do the job of ば.
If only I had the time, I could practice more.
As long as the person concerned agrees, let's go ahead with the plan.
More sentences
Even children overseas know that song.
Because of the power outage, I couldn't even send a short message.
As long as the weather is good, we can leave as planned.
As long as you get the necessary documents together, you can apply.
As long as you contact reception, they will put you through to the right department.
As long as you don't forget the basics, you can handle the harder problems too.
As long as you stay by my side, I feel at ease.