When do I use 下 vs 了 as a potential complement?

Use 下 when the main idea is whether something fits or there is enough room (capacity). Use 了 when the main idea is whether something can be done or completed (feasibility). For example, '坐得下' asks about seat availability; '坐得了' asks whether sitting is possible (e.g., due to comfort or ability).

Can 了 always replace 下 in capacity questions?

No, 了 is not natural for straightforward capacity questions. While some native speakers might use 了 in a broader sense, the standard and clear choice for capacity is 下. Using 了 can change the nuance to general feasibility rather than containment.

Are there other verbs that commonly use both complements?

Yes, verbs like 放, 装, 坐 can pair with both, but the meaning shifts. 放得下 = have room to put; 放得了 = can be placed (maybe because it's allowed or possible). The context will clarify which one is intended.

How do I negate these potential complements?

Replace 得 with 不: 坐得下 → 坐不下 (cannot accommodate); 坐得了 → 坐不了 (cannot sit/do). The negative forms follow the same pattern for all potential complements.

Easily confusedHSK 5

下 vs 了 (xià vs liǎo): potential complements for capacity vs feasibility

下 and 了 both function as potential complements to describe what is possible, but they differ in scope: 下 indicates spatial or numerical capacity (whether there is enough room to contain something), while 了 indicates general feasibility or ability to complete an action (whether something can be done). Choosing between them depends on whether you are asking about containment or accomplishment.

In Chinese, both 下 (xià) and 了 (liǎo) can be used as potential complements after a verb, but they express different types of possibility. 下 focuses on spatial or numeric capacity: it tells whether something fits or whether there is enough room for a certain number of items/people. 了 focuses on general feasibility: it tells whether an action can be completed or whether a state can be achieved, often implying a condition or limit. For example, 坐得下 asks about seat capacity, while 坐得了 asks about the possibility of sitting (e.g., if the seat is available or if you are able to sit). The two complements are not interchangeable, and the context determines which one to use.

使い分け

下xià

hold/accommodate (capacity)

Use 下 as a potential complement when the core question is about spatial or numerical capacity — whether a container, space, or surface can accommodate a certain amount or number. It commonly appears with verbs like 放 (put), 坐 (sit), 装 (load), 站 (stand), 摆 (arrange), etc. The negative form is 不下.

下 can also be used metaphorically for temporal capacity in expressions like 时间安排得下 (schedule can accommodate), but this usage is less common and often overlaps with 了.

了liǎo

able to (potential)

Use 了 as a potential complement when the main concern is whether an action can be completed or a state can be achieved, often in spite of difficulty or conditions. It works with many verbs where the outcome depends on ability, permission, or circumstances. The negative form is 不了.

了 as a potential complement is distinct from the perfective particle le. Here it is pronounced liǎo and expresses possibility, not completion. It appears in fixed expressions like 不得了, 受不了, 做不了, etc.

ひと目で分かる

	下	了
Core meaning	Spatial/numerical capacity	General feasibility / ability to complete
Example verb pairing	坐 (sit), 放 (put), 装 (load), 站 (stand)	坐 (sit), 吃 (eat), 做 (do), 办 (handle)
Question type	Is there enough room for N?	Is it possible to do X?
Negative form	V + 不下 (cannot accommodate)	V + 不了 (cannot be done)
Typical context	Containers, rooms, vehicles, surfaces	Tasks, abilities, conditions, events

例文

下
这个房间坐得下十个人。
Zhè ge fáng jiān zuò dé xià shí gè rén.
This room has enough room to seat ten people.
Uses 下 to emphasize capacity of the room.
下
书架上放得下这些书吗？
Shū jià shàng fàng dé xià zhè xiē shū ma?
Can the bookshelf hold all these books?
Asks about spatial capacity of the shelf.
了
我坐得了两个小时，你放心吧。
Wǒ zuò dé le liǎng gè xiǎo shí, nǐ fàng xīn ba.
I can sit for two hours, don't worry.
Uses 了 to indicate feasibility of sitting for a duration, not capacity.
了
这么多菜我吃得了。
Zhè me duō cài wǒ chī dé liǎo.
I can eat all this food.
Expresses ability to complete the action of eating.
下
座位不够，很多人坐不下了。
Zuò wèi bú gòu, hěn duō rén zuò bú xià le.
There aren't enough seats; many people cannot sit down (no room).
Negative form 不下 emphasizes lack of capacity.
了
我坐不了那么久，腰疼。
Wǒ zuò bù liǎo nà me jiǔ, yāo téng.
I can't sit that long; my back hurts.
Uses negative 不了 to express inability due to condition.

よくある間違い

Using 不下 when you mean 'cannot do something' (e.g., '我吃不下' means 'I cannot eat any more' due to fullness, not inability — but that's the idiom; for general inability use 不了).
Using 不了 for spatial capacity (e.g., saying '这个房间坐不了十个人' meaning 'the room can't sit ten people' would be understood but is less precise than '坐不下').
Confusing 了 (liǎo) with the perfective particle le (e.g., writing '我吃不了' to mean 'I haven't eaten' — wrong; use '我还没吃').
Applying 下 to non‑spatial actions (e.g., '我忙得下这个项目' is ungrammatical; use '忙得过来' or '能做得了').

よくある質問

When do I use 下 vs 了 as a potential complement?: Use 下 when the main idea is whether something fits or there is enough room (capacity). Use 了 when the main idea is whether something can be done or completed (feasibility). For example, '坐得下' asks about seat availability; '坐得了' asks whether sitting is possible (e.g., due to comfort or ability).
Can 了 always replace 下 in capacity questions?: No, 了 is not natural for straightforward capacity questions. While some native speakers might use 了 in a broader sense, the standard and clear choice for capacity is 下. Using 了 can change the nuance to general feasibility rather than containment.
Are there other verbs that commonly use both complements?: Yes, verbs like 放, 装, 坐 can pair with both, but the meaning shifts. 放得下 = have room to put; 放得了 = can be placed (maybe because it's allowed or possible). The context will clarify which one is intended.
How do I negate these potential complements?: Replace 得 with 不: 坐得下 → 坐不下 (cannot accommodate); 坐得了 → 坐不了 (cannot sit/do). The negative forms follow the same pattern for all potential complements.