. . :
AD: Qd = C + I + G + NX.
: . , (.. closed economy).
: 60%. (.. ), , . , .
, ( ) [1]. (business savings) ( ) ( ):
NDI = GDP Dep. T = C + Sh/h, (3.1)
S = Sh/h + Sbus. + Sgov. = Spriv. + Sgov., (3.2)
NDI (net domestic income)
Dep. (depreciation)
T (taxes)
S -
Sh/h ,
Sbus. ,
Sgov. ,
Spriv. .
.
, : , . , , . , . : , .
腻 , , . , . , , ( , luxury good). :
a> 0, 0 <c< 1, (3.3)
Yd (disposable income)[2],
c (marginal propensity to consume, MPC).
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- . . : . , , , , . [3].
, (puzzles). , . . , [4]:
(3.4)
, , . . , , , , . . , , , . . , a , , , . , , , () .
1950- . . ( 1870- 1940- .); . 45. , : . . , , , .
, , . , [5].
.
, T . Qt, t= 1 ,,T ( ). , . (bond, B), r . 1 , . , , . , , , . , , .
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Yt Qt :
(3.5)
Bt t, t+ 1.
. . , :
. (3.6)
, S = Y C , :
. (3.7)
, (, , ).
( ), :
. (3.8)
(3.8) , , .. , . (3.6):
Þ . (3.9)
(3.9) : (discounted value) W 1 (.. )[6].
, , . , , . - :
(3.10)
u(Ct) = ln Ct ,
d - .
(3.10) (3.9) :
. (3.11)
(3.11) (optimal consumption path):
, . (3.12)
, , , . , , () . , ( ), .
. .
, [7]. .
(C 1, C 2):
. (3.6)-(3.8) , :
. (3.13)
(3.13) :
. (3.14)
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, (3.12) :
. (3.15)
Q 1 c C 1 , (borrower) (lender) : Q 1 > C 1, . - 3.1.
Q 1, Q 2 r. Q 1, Q 2 [8]. , C 1*, C 2*. Q 2 , Q 1 .
, , . (Q 1, Q 2), r. , . , , , , . , () . (. 3.2). , , ( ). , , , [9]. .
, , . , , , , , . , , . , , . .
.
(life-cycle hypothesis), 1950- . (Modigliani) . , , . , , (.. ).
: , . , , , . , . :
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. T , R<T Y. , W. , .. . :
, (3.16)
g 1, g 2 .
, (3.16) . (3.16), :
(3.17)
W ,
Y ,
b ,
a .
. , (average propensity to consume):
. (3.18)
. . ( ), [10].
(3.17) a = aW, . a - : , . , , (. 3.4).
, . , : , . , , . : , , , , , .
.
1957 . , (permanent income hypothesis). , YP YT ( transitory):
. (3.19)
, , , . . , , . , .
, , , . , , :
. (3.20)
, . . , . , , . ( ) . .
, , . (3.3):
a> 0, 0 <c< 1,
, (, ), , (.. ). , (.. , ), . , - , , . a.
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. . . (3.12) [11]:
. (3.21)
. , , , C=YP. , . :
Þ . (3.22)
(3.21). , , . , . - , , ,
, . , , , (, ). , . (liquidity constraints). . - , . , (. 3.5). [12].
, .
, ( ) , . . , . : , .
, , [13].
[1] , : ( ), .
[2] , .
[3] (micro foundation) (, ). , . ( ) .
[4] , , , , , , .
[5] . , . . .
[6] B 0 (bequest) BQ T:.
[7] , , , B 0.
[8] , . , .
[9] : , , . , , - (, ) , , . . , .
[10] . ( ) , .. . ; . , .
[11] (3.16) (3.21) Qt ( R ) . W.
[12] . : .
[13] : , . , . , . . .