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If an indifference curve shows quantities where a consumer's utility from consuming two goods are equal, then why are there infinitely many indifference curves? From the diagram, you can have Q1,Q2 on IC1, but then you'd have Q1,Q3 on the other indifference curve, wouldn't that mean the consumer would receive the same utility from consuming Q1 and Q2 as well as if he had consumed Q1 and Q3, i.e. for a given Q1, the consumption of Q2 gives the same amount of utility as Q3? Shouldn't this mean that the indifference curve should be unique?

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  • $\begingroup$ "wouldn't that mean the consumer would receive the same utility from consuming Q1 and Q2 as well as if he had consumed Q1 and Q3" Why do you think this...? $\endgroup$ – Giskard Jan 21 '17 at 12:38
  • $\begingroup$ @denesp If the consumer is receiving 5 utilities from consuming q1 and 5 utilities from consuming q2, and q3 > q2, then how can he be receiving a 5 utilities from q3 as well? But isn't this what IC2 is suggesting, that the total utility of (q1,q2) is the same as (q1,q3)? $\endgroup$ – user98937 Jan 21 '17 at 12:42
  • $\begingroup$ Why do you think he is receiving a 5 utilities from q3 as well? That is not in the definition of IC2 at all. $\endgroup$ – Giskard Jan 21 '17 at 12:43
  • $\begingroup$ you do net get 5 utils from consuming q1! you get, let's say 5 utils from consuming the bundle {Q1,Q2}. You only get the same utility if {Q1,Q3} is on the same IC, but it isn't. I don't exactly see where the confusion is, but note that Q2 and Q3 are different quantities of the same good, otherwise we needed a 3-d graph. $\endgroup$ – Chris tie Jan 21 '17 at 15:36
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Utility is constant for all points $(q_B,q_A)$ on an indifference curve. So there is a number $u_1$ such that $$ \forall (q_B,q_A) \in IC_1: \ U(q_B,q_A) = u_1. $$ Similarly there is a number $u_2$, such that $$ \forall (q_B,q_A) \in IC_2: \ U(q_B,q_A) = u_2. $$ If $IC_1 \neq IC_2$ then $u_1 \neq u_2$.

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