經濟學者對saving 同investment的定義有咩唔同?

1 向銀行做按竭買新屋
investment> borrow for buying a new house
As the hosue will have the potential ability to appreciate in the future, this current investment( buy the house) will make us generate a more stream of income in the future > increase our overall wealth


2 向銀行借1000蚊 用係pizza的快遞服務。
consumption> spend $1000 to consume the delivery services at present

according to my knowledge in keynesian model,
actual investment = actual saving in the reality
planned investment + uninvented inventory investment= actual investment

according to IS-LM model,
interest rate(r) and investment(i) is inversely related,
national income(y) and saving (s) is positively related,
when r=y, that is IS curve, which i=s also

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Micro-econ的定義上:
saving is 「non-consumed income」;
investment takes place when 「people sacrifice present consumption for future consumption」.
在微觀中, 兩個字係無分別的。

但在Macro中, 例如在凱因斯模型中,
就只有在 2-sector model的expose sense; 或者當市場處於equilibrium的情況下, investment同 saving才會相等; 原因係有可能有外國資金界入。
(即係, 本地人儲錢, 可以不是用來投資, 只是
(1)作本地投資; (2)持有購買力留待日後使用; 或(3) 在外國進行投資。)
這樣, 最終有可能 investment和 saving並不相等。

2007-02-21 11:24:37 補充：
1. 向銀行做按竭買新屋銀行係做investment, 因為銀行係放棄左筆錢的其他用途, 而借左俾你。至於買家, 如果係自住, 就不一定是投資 --- 如果買樓係用來保值的, 都可以算係儲蓄; 而如果想用來衍生收入的(出租), 咁就係投資; 純粹用來住, 就兩者皆不是, 而是消費(consumption)2. 向銀行借錢買野由於買的, 屬於消費者物品(consumer goods), 除非打算會轉手賣出(investment), 否則正常而言, 這應該是消費而不是儲蓄或投資。但係銀行肯借錢俾佢, 咁這一處便可算作銀行的 investment

in classical model
saving = supply of loanable fund
investment = demand of loanable fund
係一個interest rate determination

in mircoeconomic,
saving is equal to investment. it is forgoing the present consumption for a higher future income.

in macroeconomic,
saving is equal to investment in equilibrium, saving is equal to investment is a situation to determine the national income an interest rate

1 向銀行做按竭買新屋
It is a consumption if u live in the house , it is saving and investment if u want to sell it in a higher value.

2 向銀行借1000蚊 用係pizza的快遞服務。
It is a consumption