 consumer demand. What is consumer demand that we mostly are going to discuss in our various topic? How we can assess that this is the demand of a consumer? So, in short, the willingness or the ability of the consumer to purchase the quantity of a commodity or a service in a given period of time. And if we look at it, then there is a difference between the want, the desire, or like this thing. There can be something that is very necessary, which we call the need. At the same time, we say that the consumer wants it. But in the economic system, whatever the consumer will demand in the market will be called its demand. So, when we measure its ability here, we see that only by asking for anything, it will not entail the consumer demand, rather until and unless the human demand is backed by the purchasing power. So, purchasing power means the consumer is having certain amount to pick the amount from the market. He is having something in his pocket. That is the reason we say that the consumer demand will be exhibited when the consumer, he enters the market. Here, we can see from that picture that there are the various factors in the available scenario that determine the human consumer demand. We can see that there are many other factors that do not include the price. There can be the need, there can be the income and the preferences, the expectations and different habits of the consumer as well. And when we include all these, we say that this becomes the non-price factor of the consumer. And on the other side, the one thing that is the consumer when comes to the market, as soon as the market reaches it, compared to all these factors, the first thing is the price that determines, so with the exchange of all these factors that becomes under the demand and when it is overlapped by that price factor, we say that it actually makes the consumer demand. And at the same time, the two other things that he has to see, not only the price of its own good, rather he has to face the price of its substitute and the price of the complements. What are the various factors that affect the consumer demand? As we know that the consumer is not having only one preference, so consumer may have different preferences and not only the different preferences, because consumer or market has many different commodities. So for those different commodities, the consumer's demand function may be different from each other. Now, if the value of one commodity is more in the morning and more in the evening or in the other days, then with the change in that price, the consumer's demand can vary for the same commodity as well. So, we can say that consumer have different set of prices and income and these different set of prices and income will shape his consumer demand. So, the demand function depends upon prices and income in a manner that it will include the price of that good and the price of the other goods and the income. So, consumer demand function will actually see the function of the consumer relating to his optimal choice. Now, we see that what is the optimal choice? Optimal choice when he is having various bundles and out of those bundles, one bundle that he is going to select, so that commodities, that quantity that the consumer has selected at given level of the prices and at his given level of the income that will be his consumer demanded bundle. So, it means when the consumer's demand is depending upon income and the price, so whenever this income and the price it will change, consumer demand will change or we can say the optimal choice of the consumer it will change. So, here are the case when the consumer's demand is going to change as we know that the commodity that the consumer is going to purchase from the market, it may be different in the nature. So, when in a bundle, consumer is having two commodities and these two commodities they are substitute to each other. So, we can say that X1 and X2 they both are perfect substitute. So, when the both commodities they are perfect substitute to each other and there is a case that the commodities price of P on the Y axis it is greater and commodity on the X axis having the less price as the both are perfect substitute consumer will prefer to have that commodity that will be less burden on him. So, he will have more on X axis for this he will have a flatter slope of his budget line. When the price of commodity on X axis it will be more consumer will shift its demand to the other. So, in this way the budget line it will become steeper and when the both commodities are having the same level of the price then the consumer is having the liberty to select from any type of the bundle that is joining from commodity X1 to commodity X2 line axis. So, in the diagram when we see there are the various type of the bundle available to consumer when he is having this type of the situation and we see in the diagram that if consumer will have a commodity whose price here that it is less than the price to the commodity will be selected on X axis if consumer will have the commodity price less on Y axis then consumer will shift here and if the consumer's price will be equal to price to. So, consumer may select any part of the commodity between these two lines and hit like this the optimal choice of the consumer that we see that the consumer is going to exhibit it depends always on one point where the consumer is having related to the budget line. So, when the commodity will be not the substitute rather it will become the complements. So, keeping in view the properties of the complements we know that for that commodities consumer always utilize them in a very fixed level of the proportion. So, that fixed proportion that is available to the consumer. So, whenever there will be change in the price of a commodity X 1 there will be no effect on the purchase of the other commodity because consumer has to purchase this bundle always in the fixed proportion. So, whatever the change in the prices of the commodities there will be no change on the consumer demand, but if there is the change in the income then there can be the change in the consumer demand and that consumer demand will change when the consumer has to purchase a bundle only available on the vertex or the diagonals available to him. When we draw this diagram we see that the consumer is having one indifference curve like this and the other like this and available like any to this. So, keeping in view the budget line we see that up to this budget line consumer is having the optimal choice at this level. At this level we see that if there will be any change in the price of the commodity X 1 then it means the slope of the budget line it may vary like this. If there will be the decrease in the price of X 1 whatever there will be the price change in the X 1 or there may be that any change in the price of X 2 like this. So, again here it will become there will be no point of optimal choice to the consumer, but if there will be the change in the income right side shift it means consumer income is going to increase or left side shift like this or consumer income is going to decrease. Consumer will select only the optimal choice bundle that is available up to the consumer available on the budget line and also in the fixed proportion. So, at this point we see that the tendency of the two it occurs so consumer can have the consumer demand like this.