Inheritance and capital income taxes are similar in the optimal taxation framework. Researchers have studied whether it's better to tax future consumption and estates more than present consumption. They found that taxing capital income is like taxing future consumption, so it may not be necessary if consumption elasticity is constant. However, in models with life cycles, it may be optimal to tax capital income. The same reasoning applies to estate taxation, where taxing estates may be justified based on different factors like separability between estate spending and leisure, or differences in consumption elasticities between donors and recipients. So, taxing capital income doesn't always mean taxing estates is also optimal.