Does the grammar underlying 为期 generalize to 为主, 为基础, and so on?

Question

I'm looking at the word:

CC-CEDICT: 为期 (wéi​qī​): (to be done) by (a certain date) / lasting (a certain time)

Most examples I've seen are like this:

课程为期五周。
The course runs for five weeks.

but with various nouns and time periods. It seems it is also possible to use the 以……为…… construct, such as in Pleco's example:

以三个月为期
for a period of three months

So there's two ways of phrasing it, 为期[time] and 以[time]为期.

Using the 以……为…… construct, we can form phrases such as 以教育为主 or 以农业为基础. I'm not sure if it's legitimate to mimic the grammar for 为期 and thus form phrases such as the following:

以三天为期 → 为期三天
以教育为主 → 为主教育
以农业为基础 → 为基础农业

Maybe 为期 is a special case, in that we can say 为期[time], but we can't do the equivalent for 为主, 为基础, and so on.

Question: Does the grammar underlying 为期 generalize to 为主, 为基础, and so on?

Answer 1

不可以。题主举的三个例子中，「为期」是比较特殊的。我认为原因在于「为期」这个词本身的释义。「为期」在 教育部《重編國語辭典修訂本》 中，释义如下：

1. 作為期限。《詩經．小雅．采綠》：「五日為期，六日不詹。」唐．裴鉶《傳奇．裴航》：「願以百日為期，必攜杵臼而至，更無他許人。」
2. 指時間、期限。如：「為期甚遠」。

可见，根据第一个意思，「五日為期」中的「某某为期」是「以某某为期」（将某某作为期限）的省略，「以三天为期」就是「将三天作为期限」的意思。「以某某为基础」「以某某为主」，都是这种结构。

而「为期某某」，是根据第二个意思来的，此处「为期」作纯粹的名词解释，不同于上处的语法结构。

我不清楚为什么「为期」这样的介词短语衍生出了可以作为名词的义项，而「为主」「为基础」没有。但是，事实如此。

Answer 2

"以三天为期" and "为期三天", while sounds similar, their implications and uses are quite different:

以三天为期/为限 = 限期三天, the speaker is setting a date limit to someone.

• 你必需達標, 以三天为期 = 限期三天, 你必需達標 - You must achieve the goal within 3 days. ("3 days" is the date limit)

• 這個租約以三年为期 - this rental agreement is limited to 3 years. ("3 years" is the length limit of the rental)

It differs from 为期三天, as "为期" means "the length/duration".

• 全部課程为期三天 - the full course, (start to end), will be taught in 3 days. ("3 days" is the length/duration of the course)

• 這是一個为期三年的租約 - this is a 3-year rental agreement. ("3-year" is the length/duration of the rental)

The pattern 以xx为yy is particularly useful for talking about "setting xx as priorities", and it is not flexible grammatically:

• 以"教育"为主; 以"農業"为基礎; 以"xx"为榜樣; 以"xx"为榮/恥....etc.

Answer 3

All generalisations are necessarily untrue.

为主: as main (something): 为主(食)
在一些国家，人们以土豆为主(食)。
In some countries, potatoes are the basic foodstuff.

为基础: (something) as basis:
公寓租金按(全部住满)为基础计算。
The apartment rent is calculated based on full occupancy.

Answer 4

[以]XX[为]YY = [with] XX [as] YY

Examples:

[以]三个月[为]期 = [with] three months [as] duration

[以]教育[为]主 = [with] education [as] primary

[以]农业[为]基础 = [with] agriculture [as] basis

[以]美国[为]首 = [with] America [as] leader

However, 为期 can also be a compound word constructed with [为 + 期] meaning "duration set for"

Example:

[为期]三个月 = [duration set for] three months

Similarly:

[以]三千元[作]价 = [with] $3,000 [as] price

[作价]三千元 = [priced] at $3,000