When marginal rate of substitution is increasing, the indifference curves become concave to the origin.
In case of perfect substitutes indifference curves take the shape of negatively sloped straight lines.
When two goods are perfect complements, the indifference curves take the shape of right angles. Normally, indifference curves are convex to origin, they are neither straight lines nor right angles.
When one of the two goods has zero utility, the indifference curve becomes horizontal to the axis on which good with zero utility is measured.
When one of the two goods is an absolute necessity, the indifference curve gets steeper as it approaches the axis on which the good of absolute necessity is measured.
When one of the two goods has a negative utility, the indifference curve becomes U – shaped.
When one of the two goods is not consumed at all, the IC will touch the axis that measures the good on which the entire income is spent and becomes flatter as it moves towards the other axis.
