ある and いる contrast each other in many ways. There are some important exceptions to conjugation that you need to keep in mind.
|Verb||Class||Plain Negative||Polite Negative||Plain Negative Past|
Grammar Note: The negative of ある is ない, not あらない. This is not the only anomaly in regards to conjugation for these two verbs, but for now, just keep this in mind.
Both ある and いる show that there is something. They may or may not be interchangeable depending on their use. Even when can choose between the two, one will always be more prevalent/natural than the other. ある normally shows existence of things besides people and animals. 存在する is more appropriate, especially with non-physical items, for the explicit meaning of "to exist."
Particle Note: に, not で, should be used with existential verbs. で shows location of action, not state. Existing in a place is a state of being. Furthermore, をある and をいる are always wrong.
There was a wallet there.
There is a tall tree.
There are a lot of tall trees in the park.
Is there a public telephone?
There is a hospital in the city.
The main office is in Tokyo.
The new product is not in the trial stage.
8. 両国間には国交がありません。 (Not Spoken Language)
There isn't any diplomatic relations between both of the nations.
There are police stations at intersections in Japan.
In Nagoya, there is the Nagoya Castle (but not anywhere else).
Culture Note: The Nagoya Castle was one of the most important stops on the Minoji 美濃路Highway which was a major roadway in the Edo Period. The castle is historically significant.
Isn't there a firm handle in that car?
Possession and Occurrence
ある may also show the possession of inanimate non-living and non-physical things. This usage may also show physical attributes of people and things. It can even mean "to occur". Depending on the usage of "to occur", there are alternative ways to say it. 発生する is "to occur" as in a break out of some kind. 起こる means "to occur" as in some event. For this usage で can be used because "to occur" is not existential.
A king ample in both gold and time
To have one's likes and dislikes.
There is humor in her composition.
There was an earthquake in Nara.
16a. There was an accident.
16b. I was in an accident.
There was an announcement.
To have worries.
The animal has a weight of at least 200 kilograms.
To have an acquaintance with each other.
To have an education.
There is nowhere to hide.
The height is 60 meters.
Do you have assets?
Do you have a room with a bath?
As for me, I have a strong ally.
Usage Note: This ある would most certainly almost always be replaced with いる today.
Do you have milk?
Do you have a timetable?
Old Usages: ある may be used in the introduction of characters, but いる is predominant in this case. More so literary, ある may show that someone is in a certain position/role. Again, いる is more common here. It may also be used in this manner with things, in which case いる would not be applicable.
Long time ago, there was an old man and an old woman.
The last old usage that we will look at is とある. This is not used in the spoken language. However, you can find it in the written language a lot in contexts such as in Ex. 30.
It is written in the Bible that, "In the beginning, God created the heavens and the earth."
いる shows that an animate and alive thing exists in a certain location. It may also show the possession of something animate and alive.
Mr. Sato was not home.
I don't have a dog (since it left somewhere).
Nuance Note: Using が here makes it sound like either there isn't a dog, and in the case of ownership, something happened to the dog, like it ran away, was stolen, or died. If you were to say 犬はいません, you would be able to say I don't have a dog, but it sounds like you may own something else like a cat. You could say 犬を飼っていません to avoid this extra nuance. 飼う means "to raise an animal." You could just also naturally respond with いません or 飼っていません.
We have three birds in our house.
There is the evening Venus.
Sentence Note: Ex. 34a is an example of いる in literary language that wouldn't be used in the spoken language. Originally, this usage was meant to show something that normally moves but is not.
ある VS いる Troubles
In reality, natives don't all agree with each other on case by case instances of ある VS いる. What do you use with words like 家族, バス, エレベーター, 人形, or a dead cat? None of these example nouns are necessarily straightforward.
I have a family.
Sentence Note: More speakers would choose いる. However, ある is not strange at all.
There is God/god/kami.
Sentence Note: Ignoring the various interpretations of the word 神, describing such a spiritual force's existence with いる is most common today, but ある does get used. It may sound less religious, stiff, or old-fashioned, but this Japanese does exist.
37. 私（に）は兄弟が3人｛ （△・X） ある・〇 いる｝。
I have three siblings.
Sentence Note: Using ある for people causes heart attacks for Japanese learners, but the reality is that there are speakers who find this instance of ある perfectly fine, though even these individuals will admit that it is old-fashioned.
38. 私の2人の兄弟は神奈川に｛〇 います・ X あります｝。
My two siblings are in Kanagawa.
There are a lot of dolls, aren't there.
Sentence Note: いる would most especially be used when in contact or in the vicinity of the dolls, but it's important to know that speakers use both. The decision hinges on how human-like you wish to view dolls.
There is a robot over there.
Sentence Note: If you use いる, the robot is in service and is truly human-like. If you use ある, it's in the same position as a regular inanimate object.
41. あそこにバスが｛〇・△ いる・〇 ある・〇 止まっている｝。
There is a bus over there.
Sentence Note: いる has the nuance of that it is in service, but some speakers still think that this is wrong. Other speakers think that this is even OK for elevators and what not in service, but others still disagree and believe you should use 止まっている when its stopped there indefinitely. If you wanted to show it's just stopped there, the particle に should be changed to で. If you use ある, you would simply state that there is a bus/elevator, and it would most certainly mean it's not in service.
42. 捕らわれの身｛〇 にある・X でいる｝。
To be in captivity.
Sentence Note: This is a set phrase, but the grammar is also a little tricky because にある is actually the original copula. It shows up here as set phrases tend to hold onto old grammar. However, when we try replacing it with grammar we've learned today, we see that the result is ungrammatical.
The Dead: いる or ある?
What if something is dead? Certainly, when you use words such as 死体 or 遺体 which mean corpse, you use ある. When discussing the existence of dead people, いる is overwhelmingly used. However, consider this counterexample.
There were people who died from peanut allergies.
Many speakers would not like ありました. Those that do, though, would say it is rarer, but it is more emphatic and focusing on the severity of the matter than いました. What about dogs and cats? Generally, people would hate using ある for dead dogs and cats. If you really hate either or, you could use ある. This would imply you don't value them as much.
44. 毒入りのものを食べて、死んだ猫が｛〇 いた・ △ あった｝。
There was a dead cat that ate a poison-laced item.
What about a dead fly? The phrase 死んだハエ is possible. Most would still say いる is OK and ある is not so OK, but saying 死んだハエがいる is not practical. Thus, some say that a sentence like below would be more practical.
There is a dead fly in my cup.
Another word to consider is けが人 (injured). It turns out that even if the noun is a person noun, if the concept is abstract, it can still take ある. Or, if there is any wavering of whether something exists or not, ある more easily appears.
46. 乗客の中にけが人は｛ありません 〇/X・いません〇｝でした。
There were no people injured among the passengers.