A Pigovian tax is a type of taxation that is designed to act as a market-based solution to correct for external costs, or the costs of negative externalities, not borne by the producer of goods or services. Negative externalities such as environmental pollution, noise pollution, and congestion can be costly to society at large, but not always taken into account when businesses conduct their operations. The purpose of the Pigovian tax, often referred to as an excise tax, is to create an incentive for businesses to take these externalities into account and reduce them, or pay for them, ultimately leading to an overall benefit for society.

Pigovian taxes differ from traditional taxes in that the revenue generated by the tax does not go to the government to fund public services, such as infrastructure or healthcare. Instead, the revenue goes to the companies or individuals who are responsible for the negative externalities. Often times, Pigovian taxes are set at a rate intended to equal the cost of the negative externality, although the rate is often difficult to determine. When the rate is too high, there is the risk of over-incentivizing the reduction of the externality, which could ultimately be harmful to society in some form.

In modern times, Pigovian taxes are quite common. Some examples include taxes on carbon emissions and taxes on plastic bags. Carbon emissions taxes are often used to incentivize companies to reduce the amount of greenhouse gases they produce, while taxes on plastic bags are designed to incentivize consumers to use reusable bags instead. Fundamentally, the goal of Pigovian taxes is to equalize the cost of the harm caused by the externality and make sure the negative cost is not borne by society at large.

In summary, Pigovian taxes are taxes intended to be used as a market-based solution for external costs. The goal of these taxes is to incentivize companies and individuals responsible for negative externalities to pay for them instead of allowing society to bear the cost. This can be done by setting the tax at a rate equal to the cost of the negative externality. Examples of Pigovian taxes include taxes on carbon emissions and taxes on plastic bags. Although Pigovian taxes can be a powerful tool to ensure that costs caused by externalities are properly allocated, it is important to make sure the rate of the tax is not set too high and risk leading to an adverse outcome.