Learning to differentiate the subtle nuances between 〜ている, 〜てある, and 〜ておく might be one of the biggest headaches for Japanese learners. Not only do they look similar, but they can all serve a similar purpose, too: these grammar patterns describe a situation created by some intentional action done in the past. Despite their similarities, each pattern emphasizes or implies something different, such as an action being done in preparation of something, or remaining in the state the action created.
Let's say you usually leave the window open at night to let in some cool air. To tell someone about this habit, you can use either 〜ている, 〜てある, or 〜ておく and say:
- いつも夜は窓を開け [ている・てある・ておく] 。
- I usually keep the window open at night.
See how they all describe the state of the open window, which was created by the action of you opening the window? In that way, the three expressions can work very similarly.
But what exactly is the difference between these expressions, and how would you choose which one to use? The extra nuance that's implied by each is reflected in the translations below, so check them out to see what each sentence sounds like to a native speaker.
- I usually keep the window open at night.
- I usually keep the window open at night (so it won't get too hot).
- I usually keep the window open at night (so that I won't have to worry about getting too hot and waking up in the middle of the night).
So you can see there are some subtle differences in the nuance here. But don't worry if the distinction is still a bit hazy. The good news is that 〜ている, 〜てある, and 〜ておく aren't always interchangeable. (At least, we hope that's good news.) Like the previous example sentences, each pattern has its own set of implications, making it better suited to certain situations than the others. This article will help you learn more about these basic distinctions, so you'll be able to understand the subtle differences in nuance in the uses that overlap one another.
- The Basic Concepts of 〜ている, 〜てある, and 〜ておく
- So…What's the Difference In Situations When They're All Interchangeable?
Prerequisites: This article assumes you already know hiragana and katakana. If you need to brush up, have a look at our Ultimate Hiragana Guide and Ultimate Katakana Guide. Although this article starts with a basic explanation of each grammatical pattern, you may also want to check out our grammar pages on 〜ている, 〜てある, and 〜ておく for a more detailed background explanation on each expression, as this article focuses more on deeper nuances. Additionally, knowledge about transitive and intransitive verbs is a plus, since we'll also be discussing transitivity in order to explain the differences between 〜ている, 〜てある, and 〜ておく.
The Basic Concepts of 〜ている, 〜てある, and 〜ておく
Let's begin by comparing the basic concepts of 〜ている, 〜てある, and 〜ておく. We'll get to some examples later on, but here are the fundamental concepts behind each pattern:
〜ている:When connected to a verb, this expresses an ongoing action or a continuous state initiated by an action in the past.
〜てある:When connected to a verb, this describes the current state of something while often hinting that the situation was previously devised intentionally.
〜ておく:When attached to a verb, this implies the action is taken to complete a task in preparation for something, in order to "put" (the verb 置くmeans "to put") it out of your mind. Depending on the tense, it can refer to an action you're going to take or have already taken. It can also denote the state of things after completing a task.
The key differences between the three are the nuance, the level of intention, and whether the focus is on the action itself, or a situation that is the result of that action. We'll be discussing all these key differences throughout the article, so don't worry if you are not getting it just yet.
Next, let's take a closer look at how each pattern works while applying the concepts noted above.
〜ている is the plainest and most neutral of the three patterns. It has two functions: it can describe a continuous action, or a state which is the result of a previous action. One way to think of it is as expressing a sort of "activation mode." What 〜ている does is express an ongoing situation that's "activated" by something that happened or that has started happening. Let's take a look at some examples of ～ている to see how it works.
Describing Things That are Currently Happening
First, let's quickly go over how to use 〜ている to talk about something that's currently happening. For example, say you're working in the kitchen and your kid comes in to ask what you're doing. In this scenario, you might say:
- I'm making bento right now.
This expression works similarly to the present continuous ( -ing ) in English, which shows that an action is happening at the same time as it's being spoken about.
Here, 〜ている is used to indicate that you are in the process of "making a bento." The implication is that it's still underway, but you've already started the process. You started cooking, and so the act of cooking has been activated.
Also be aware that particle を is often omitted in conversation, but we'll keep it in this article so that the sentence structure is easier to understand.
This is the most common function of 〜ている, but when used like this it can't be replaced with 〜てある or 〜ておく.
Describing the Resulting State Activated by a Past Action
In addition to describing something that's currently happening, 〜ている can also be used to describe a situation or condition that is the product of a past action or event. In this use, 〜ている often functions like an adjective because it's used to describe the way something is.
Let's say your kid finds a bento box that's been left on the kitchen counter with the lid open. They tell you:
- The bento lid is open.
Notice that 〜ている is used differently from the previous example. 開く is an intransitive verb that means "to open," but in this sentence the 〜ている form it means "to be open," rather than "opening."
〜ている often functions like an adjective because it's used to describe the way something is.
This is because the verb 開く usually indicates an instantaneous change. Once the lid has begun to be opened, the "opened state" of the lid is "activated." With verbs that change the state of something instantaneously like 開く, using the 〜ている form allows you to describe the state of something that resulted from the change instead of an ongoing action.
Why? Because with an intransitive verb like 開く, there's no implication beyond the bento lid being open. It only describes the bento lid being open, while not focusing on who performed the action. Remember, 〜てある and 〜ておく always imply that there is intention or purpose behind the action being described. So without this implication, you can't swap 〜てある or 〜ておく for 〜ている in this example.
Describing the Resulting State Activated by an "Intentional" Action
In the previous section we covered that when used with an intransitive verb, 〜ている isn't necessarily interchangeable with 〜てある/〜ておく. This is because with intransitive verbs there's no indication of the action being described as intentional. But how about a transitive verb? Let's take a look at another example, continuing the bento scenario.
Suppose you're leaving the bento lid open on purpose. But since your kid is commenting on it being open, you want to tell them that it was intentionally left open so that they don't close it. So you say:
- I'm leaving the lid open!
Here, notice the verb is 開ける, which means "to open something" — the transitive version of 開く that you saw earlier. With 〜ている, this sentence could mean you're "opening the lid" if that's what you are currently doing — i.e. your hand is on the lid and about to remove it — but it's clearly not the situation here. Rather, this is a response to the question about the lid that's already been opened, so it describes the bento box being left open, which resulted from your past intentional action of opening the bento and leaving it that way.
You might have also noticed looking closely at the example that the expression used is てる instead of 〜ている. It's not a typo — both forms are grammatically correct. 〜ている is usually shortened in casual conversations. 1
Out of the three uses of 〜ている, this is the only one that can be used interchangeably with 〜てある or 〜ておく (or rather 〜ておいた, the past tense). That means you could also use 〜てある or 〜ておく to explain that you intentionally opened the lid and left it that way, like this:
フタ、開け [てある・ておいた] んだよ！
Why? The short answer is that this use of 〜ている implies an "intention" and you can tell that by the context. We'll get into a deeper comparison of ～ている, ～てある, and ～ておく in a bit, so for now, just keep in mind that this very specific use of ～ている is the only one that can be interchangeable with the other two.
〜てある indicates that the situation was caused intentionally, often for a particular purpose.
Now on to 〜てある. First of all, 〜てある describes the current state of something with the implication that someone did something to it earlier and left it that way. That "someone" can either be yourself or someone else, depending on the particle that precedes it.
It's also important to note that 〜てある is always used with a transitive verb, because a transitive verb is a type of verb that indicates an intentional action.
〜を〜てある for a Situation Caused by Yourself
As I briefly mentioned, 〜てある can be used when describing a situation that resulted from either your own or someone else's action. And there's an easy way to differentiate between the two: each uses a different particle.
Before we really get into the mechanics of things, let's circle back to using 〜てある to describe a situation that's the result of your own action. Remember the bento example from earlier? We mentioned that you can use 〜てある to explain that you opened the bento box and are leaving it open, like this:
- I'm leaving the lid of the bento box open.
Although を can often be omitted in spoken Japanese, this 〜を〜てある pattern is the structure used when talking about a situation caused by yourself.
In this example, を marks the lid as the object of the sentence. This means that the likely subject, although not clearly stated, is the speaker, or 私 meaning "I," which can be understood from the context.
Let's carry on the bento-making scenario for another example. Trying to think of something that will pair nicely with the bento for dessert, you remember that you bought some yogurt to have on hand for an occasion like this. In this case, you can use 〜てある and say to yourself:
- There's some yogurt (because I bought some).
Remember that you can also use 〜ている or 〜ておく to express something similar. We'll talk about this in more detail later on.
〜が〜てある For a Situation Caused by Someone Else
One unique aspect of 〜てある is how it can be used to describe a situation that's caused by someone else.
Take for example a situation that's slightly different from the previous one — you come across some yogurt in the fridge when looking for a dessert for the bento. But in this case, you are not the one who bought it. You might say something like:
- There's some yogurt (that someone must have bought)!
What 〜てある is doing here is describing that the yogurt is in the fridge, while also implying that someone (not you) bought it earlier. While the sentences are nearly identical, the difference is in the use of particles.
This might feel tricky, but here's a tip. Think about ある at the end as the verb used for non-living things' existence. The verb ある pairs up with が and indicates "there is…" right? So ヨーグルトがある means "there's some yogurt," and this is just describing what's there objectively. ヨーグルトが買ってある is similar to this, but it just adds the implication that the action ("yogurt was bought," in this case) was performed by someone besides you.
Just like 〜がある, you are describing the situation sort of objectively because you were not involved in the action — someone else was. And just like ある often expresses the sense of realization when it's paired with the subject marker が, 〜てある carries the nuance that you came to a realization, too. So ヨーグルトが買ってある hints that it was a surprise to you (and it was a nice one).
And just like ある often expresses the sense of realization when it's paired with the subject marker が, 〜てある carries the nuance that you came to a realization, too.
To summarize, 〜てある can take the particle が to mark something that's seemingly an object ("yogurt," in this case) even though it is used with a transitive verb. And when it does that, it implies that someone other than you performed the action that resulted in the state it describes. This is something unique to 〜てある, and what makes it different from 〜ている and 〜ておく. In other words, ヨーグルトが買っている or ヨーグルトが買っておく are not valid sentences — actually, these sound like yogurt is the subject who's buying (something). It'd be super weird unless the person's name was Yogurt (which would certainly be a twist).
〜ておく can serve two functions depending on the tense. In the present tense, it sounds as if you are completing a task for future convenience so that you can "put" it out of your mind. On the other hand, in the past tense, 〜ておいた denotes the state of a completed task.
ておく For Future Actions To Complete Tasks
Especially used in the present tense, 〜ておく is a little different from the other two patterns discussed so far. While 〜ている and 〜てある can be used to describe the current state of things, 〜ておく indicates a future action. Specifically, the future completion of a task so you can "put" it out of your mind.
For example, if you're currently in the process of making a bento and decide to leave the lid off to let some steam out, you can use 〜ておく and say:
- I'll leave the lid of the bento box open (to let the steam out so I won't have to worry about it getting musty and spoiling).
It's a slight difference that's important to note here between using 〜ておく in the present tense and the previous examples with 〜ていく and 〜てある. Where they were used to describe a situation where a bento box is left open intentionally, here 〜ておく is indicating your (very near) future plan of leaving the lid open.
You're using 〜ておく because you want to express that you're doing this for your future convenience.
In this case, you want to let the steam out to prevent it from getting musty inside the bento box.
You might be wondering "Why does 〜ておく indicate a future action, not the current state of something like 〜ている and 〜てある?" Well, it might help if you think of it like this. 〜ておく comes from the verb 置く meaning "to put." Just like any other action verb, when used in the present tense, it can indicate a future action, in addition to a general act or a habit.
In comparison, think about 〜ている and 〜てある, and their roots — the verbs いる and ある. These verbs are a bit special, differing slightly from regular action verbs in that they indicate the existence of things, or describe the way things are rather than something that needs "doing." Hopefully, that helps you better understand how 〜ておく works in the present tense.
Now, let's take a look at another example. Say you're at the grocery store to buy yogurt for your bento. You can use 〜ておく and say:
- I'll buy some yogurt (to add to my bento).
Here, 〜ておく carries the nuance that you're going to do something in order to "get it done," or out of the way. And again, note that it's the future action or plan that you are using 〜ておく to describe.
ておいた For Completed Tasks
So far, we've discussed the differences in the nuance of 〜ておく in the present tense to talk about a future action. Now let's take a look at how it's used in the past tense (〜ておいた) to talk about a current situation that is the direct result of an action performed in the past, i.e. something you took care of in the past that resulted in the present state of things.
Let's bring back the previous example of leaving the bento box lid open. To say you left it open, you need to conjugate 〜ておく to the past tense and say 2:
- I left the lid of the bento box open (to let the steam out so I won't have to worry about it getting musty and spoiling).
In this case, the focus is more on your past action (opening the lid), but it can also indicate the current state resulting from the action (the lid is left open), depending on the context.
Now, remember that yogurt from before? If you want to mention that there's some yogurt for the bento because you bought it earlier for that purpose, you can use 〜ておいた and say:
- I've bought some yogurt (for bento making).
Although these situations can be described in a similar manner using 〜ている or 〜てある, let's not forget the special nuance of 〜ておいた — it always implies that you performed an action with the intention of causing the current situation because you wanted to get something out of the way. In this case, maybe you felt you needed to have a backup bento filler and to serve the purpose you bought some yogurt. So this stresses that you bought the yogurt in preparation for the future. As a result, out of the three patterns 〜ておいた most strongly implies your intention behind the action.
ておく For Habitual Actions To Complete Tasks
Earlier, we talked about how 〜ておく can be used to describe a future action, but that's not the only thing 〜ておく can express in the present tense. In fact, depending on the context it can also be used to express a habitual action. Remember, the root of 〜ておく is the action verb 置く ("to put"), and action verbs when used in the present tense can express a general act or habit of doing something, not only a future action. Let's take a look at one more example of ～ておく in the present tense, bringing back the first example in this article, the window:
- I usually keep the window open at night.
As you saw previously in this example, ～ている, ～てある, and ～ておく can be used interchangeably in the present tense to describe a habitual action or something you do regularly for a reason. However, there are subtle differences in nuance between them.
Of the three, 〜ておく is actually the most nuanced — it implies that you did something for your future convenience. In this case, maybe you keep the window open so you won't have to worry about getting too hot and waking up in the middle of the night. Or, maybe because your kids fantasize about Peter Pan coming through the window and taking them to Neverland.
Whatever the reason, 〜ておく implies that whatever you're describing is something you want to get out of the way.
After all, you don't want your kids waking you up in the middle of the night and complaining that you didn't leave the window open for Peter Pan, you know?
Now that we've covered all the basics, in the next section we'll take a deeper look at how the nuance changes with each pattern depending on the situation.
So…What's the Difference In Situations When They're All Interchangeable?
Now let's finally get into the comparisons of the three patterns: 〜ている, 〜てある, and 〜ておく. As a quick review, they are essentially interchangeable when used to describe the current state of something that resulted from a past action (usually something intentional).
So, what exactly is the difference in those situations when they can be used interchangeably? Let's find out by going through a few examples and comparing the nuances.
Different Levels of Intention
expresses intention less < expresses intention more
One of the main differences in nuance between 〜ている (or rather, its shortened version てる), 〜てある, and 〜ておく is the level of intention.
For the first example, let's go back to bento again. Say that you're cooking (or have cooked) rice because it's an essential element of bento.
ご飯を 炊い [てる・てある・ておいた] 。
Broken down, ご飯 is "rice," and the verb paired with it meaning "to cook" is 炊く. So what exactly is the difference in nuance when we use each different pattern?
Let's take a look at ご飯を 炊いてる. This sentence can actually be interpreted in a couple of ways. The first is:
- I'm cooking rice.
This is one of the possible translations — the present continuous use of 〜ている to explain what you're currently doing — means you are in the middle of cooking rice. (Note that 〜てある and 〜ておく cannot be used to express an action that is currently underway.)
The other possible meaning of this sentence is:
- The rice is cooked.
Remember that 〜ている can also denote the resulting state of an action, i.e. the state of the rice that is already cooked. So how do you know when it means what? That will depend on the context of the conversation. Say your kid requested a sandwich for lunch, and you say this to tell them that you already made rice. (Too late, kiddo!) This is when 〜ている is interchangeable with 〜てある or 〜ておいた.
In terms of intention, 炊く is a transitive verb, and "rice being cooked" won't happen on its own (someone's gotta cook rice, you know?) so technically speaking there is some implication of this here. However, compared to the other two patterns, 〜ている doesn't emphasize the intentional nuance as much. So this version with 〜ている sounds like you're just simply stating that you cooked the rice and the rice is ready.
Now, what about 炊いてある? As a quick reminder, 〜てある describes a situation where you did something and you left it that way for a reason.
- The rice is cooked (for a reason).
Compared to 〜ている, the 〜てある version has a stronger and clearer indication of the intention behind the situation being described, as if you are saying, "I cooked rice for a reason." This version is commonly used when you want to draw attention to something you've done and specifically left that way. In other words, this almost sounds like a heads-up or the reason for things being the way they are.
The reason could be for making onigiri, or whatever other reason you might cook rice. Implying that there's a reason for it naturally adds a more intentional nuance, especially compared to 〜ている. In that sense, this could make an even stronger statement to your kid who requested a sandwich at the last minute.
Lastly, 〜ておいた carries the strongest level of intention. To remind you, 〜ておく basically indicates the act of doing something for future convenience.
- I cooked the rice (for future convenience).
So this sentence sounds like you cooked the rice to make things easy later. Now, don't forget, 〜ておく also gives off the vibe of doing something in advance so you can put it out of your mind — like you're going ahead and marking a task off of your to-do list. It's a very nuanced expression!
〜ておく also gives off the vibe of doing something in advance so you can put it out of your mind — like you're going ahead and marking a task off of your to-do list.
Maybe you started cooking the rice first thing in the morning. It takes some time for rice to cook, and it will take some time for it to cool down so you can pack it in the bento. Once your kids wake up, you might not get a chance to rinse the rice and start the rice cooker. So, thinking about the actual process, it makes sense to cook it sooner rather than later so you won't have to worry about it not being ready in time.
You may never have given that much thought to the logistics of cooking rice, or maybe it's already a solid routine of yours, but in this sense 〜ておく implies that you had a thought process and there was some sort of planning involved. This adds more of the "intention" nuance compared to the other two patterns.
What's more, with 〜ておく the focus is actually on your action rather than the resulting situation — we'll talk more about this in the following section. This pattern stresses your contribution, whereas the other two highlight the fact that rice is cooked. So using 〜ておく emphasizes your intention slightly more than 〜てある and can even sound a little more braggy, like you're implying, "I did this for your convenience, okay?"
Situation-Focused vs Action-Focused
Another point of difference is whether the emphasis is on the action, or the resulting state or situation caused by that action. You might have noticed the slight difference in the previous example translations — "the rice is cooked" and "I cooked the rice." Technically speaking, this ultimately depends on the context, but knowing where the emphasis lies for each pattern should help you get the gist of the differences in nuance a little better.
Basically, the main difference is that 〜てある focuses on the result of the action ("the rice is cooked") whereas 〜ておく focuses on the action itself ("I cooked the rice"), and 〜ている is sort of neutral and could focus on either depending on the context.
situation-focused ⇔ action-focused
Here's an example to elaborate on what this means. Let's say you put strawberries in the bento because that's your kid's favorite fruit. To deliver this good news, you can use any of the three: 〜ている (or its shortened, more natural-sounding version 〜てる), 〜てある, or 〜ておく:
お弁当にいちごを入れ [てる・てある・ておいた] よ！
Now let's take a look at how each of these patterns can have a slightly different nuanced meaning.
- There are strawberries in the bento (because you like strawberries)!
The root verb ある means "to exist," so it's used to describe the way things are rather than the action that caused the situation.
Here, 〜てある is describing the situation, rather than the action that caused it. In other words, it describes the state of the strawberries being in the bento. It's calling particular attention to the strawberries, so the implication of you putting them there takes a back seat to the strawberries themselves in this case.
Now, you might be wondering about 〜ている because its root verb also means "to exist." It can certainly be situation-focused, but we also need to think about how 〜ている is also used to refer to an action, especially continuous action. We'll talk more about this in the following section.
- I am putting strawberries in the bento!
There are strawberries in the bento!
〜ている can be both situation-focused and action-focused, and the focus varies depending on the context. This is because 〜ている has two major functions — one that emphasizes the action itself (continuous action), and one that focuses on the situation caused by the action (resulting state). In this particular example, 〜ている can indicate the "action," such as what you're currently doing ("I'm putting strawberries in as we speak"), or the state where "strawberries are in the bento."
We mentioned that the focus of 〜ておく is on the action itself, which in this case is "putting strawberries in the bento."
- I put strawberries in the bento (because I know you'll enjoy them)!
This means that 〜ておく is used to talk about an action taken with the intention of creating a certain situation, whereas 〜ている and 〜てある describe the situation that's caused by the action.
〜ておく is used to talk about an action taken with the intention of creating a certain situation
It might be good to think of this from the point of view of the root verb 置く(to put) as well. 置く is an action verb, or a verb that indicates an action — "putting." By contrast, the verbs いる and ある are stative verbs meaning "to exist." There's no express action involved; they simply indicate the state of something. This might help you remember that 〜ておく is more "action-focused" whereas the other two are "situation-focused," describing how things are as the result of the action.
Talking About Your Habits
Like we mentioned earlier in the example about keeping the window open at night, 〜ている, 〜てある, and 〜ておく can be used interchangeably to talk about your habits. So let's take a look at the final nuance, comparing the three patterns when talking about habits, and then review what you've learned so far.
Say you're at the park talking to another parent while your kids are playing. But it's awkward. You need some excuse to leave so you casually drop in something about your daily schedule and say:
- いつも、６時にはお風呂をわかし [てる・てある・ておく] んだ。
- I usually have the bath ready by 6 p.m.
Again, all three patterns are interchangeable here, but with a very slight difference in nuance between 〜ておく and 〜てある. Oh, and notice that 〜ておく is not in the past tense here but it works fine because you're talking about a general habit. Now, let's take a closer look at how each one works.
- I usually have the bath ready by 6 p.m.
I usually run a hot bath by 6 p.m.
In the same vein as describing what you're currently doing, 〜ている can also be used to describe your habits, because a habit is something you do in general (not just an action taking place in the current moment). In this case, it's also describing the resulting state of the bath being ready by 6 p.m., so it's interchangeable with 〜てある and 〜ておく.
〜ている can also be used to describe your habits, because a habit is something you do in general
Remember how 〜ている can be situation-focused and action-focused? This particular example actually feels a bit vague in terms of the focus because it's a combination of both: 〜ている describing a habitual action as well as the resulting situation. In that sense, this sentence leaves it unclear whether you start running hot water by 6 p.m. or you have it ready by 6 p.m. — It could be interpreted in both ways.
And, how else is this use of 〜ている different from the other two? This 〜ている version is simply explaining your habit of getting the bath ready by 6 p.m. Descriptive and straightforward, there's not much extra nuance to it compared to the other two.
- I usually have the bath ready by 6 p.m. (for a reason).
Here, 〜てある is describing the daily situation that you usually have the bath ready and filled by 6 p.m. Because 〜てある is situation-focused, rather than action-focused, the emphasis in this example is on the bath and it being ready and hot. It also implies that there's a particular reason, which might be kind of obvious in this case — for you or your family to take a bath. Maybe you have it ready by 6 p.m. because you like to take a bath after dinner. Or maybe to let your pet capybaras soak and swim in it. Who knows, but 〜てある implies you did it for a reason.
- I usually have the bath ready by 6 p.m. (so I won't have to worry about the bath not being ready by the time someone needs it).
〜ておく here is describing your habitual action of running the bath and having it ready by 6 p.m., emphasizing that you do so for your future convenience. Remember, 〜ておく is action-focused so it puts an emphasis on the action you perform.
The nuance of 〜ておく is that you perform the action so that you are done with the task and you can put it out of your mind. Maybe your partner comes home at 6:01 and takes a bath at 6:02 every day. You'd want to mark off this task of your to-dos so that you don't worry about messing up their daily schedule by any chance.
Starting a New Habit
We could probably prepare 100 more examples to help you master the nuanced differences between 〜ている, 〜てある, and 〜ておく, but for now let's leave it here so you can put it aside and process what you learned.
Hopefully, you have a good idea of how all three forms differ, and the implications behind using them to talk about something you're currently doing or do regularly, the current state of things, or something you prepared in advance for your future convenience.
Like many phrases in Japanese, a lot can depend on the context. But the more you practice, the more progress you'll make in mastering these forms!
Some may claim that this 〜てる is a short form of 〜てある, and that 〜ている can't be used with almost all transitive verbs. However, we believe that 〜てる is often a short form of 〜ている even when it's used with transitive verbs. For example, imagine your friend asks you if the drinks for a party are ready and you answer もう買ってるよ (I've bought them already). Here, in casual speech, saying もう買っているよ sounds off, whereas もう買ってあるよ is fine. This unnaturalness of a transitive verb + 〜ている (not 〜てる) in casual speech is probably the reason that some people claim that 〜てる is a short form of 〜てある and ている can't be used with almost all transitive verbs. However, if this conversation was held at a more formal setting, the answers can be either もう買っています or もう買ってあります, which are the polite versions of 買っている and 買ってある respectively. The difference between the two versions is that もう買っています is more action-focused whereas もう買ってあります is more situation-focused. And the short, casual version, もう買ってるよ, carries the similar action-focused nuance to もう買っています rather than situation-focused. For this reason, we believe that 〜ている can be used with transitive verbs, and we treat 〜てる of "a transitive verb + 〜てる" as the short form of 〜ている, rather than 〜てある. ↩
To talk about the current state of things, you can combine ～ておく with ～ている like this, 開けておく＋ている（開けておいている）. This usage expresses that you are leaving something open while stressing that you're currently maintaining the situation you intentionally created. Again, 〜ている often contracts to 〜てる, as in 開けておいてる. ↩