A Treatise of Taxes and Contributions Shewing the nature and measures of crown-lands, assessements, customs, poll-moneys, lotteries, benevolence, penalties, monopolies, offices, tythes, raising of coins, harth-money, excize, &c.; with several intersperst discourses and digressions concerning warres, the church, universities, rents & purchases, usury & exchange, banks & lombards, registries for conveyances, beggars, ensurance, exportation of money [&] wool, free-ports, coins, housing, liberty of conscience, &c.; the same being frequently applied to the present state and affairs of Ireland.

William Sir Petty’s "A Treatise of Taxes and Contributions" offers a comprehensive and practical examination of public finance and economic policy in the mid-1600s, with a particular focus on Ireland’s social and political landscape. The treatise systematically addresses the nature and measurement of various public charges, including crown lands, customs, poll taxes, lotteries, benevolences, penalties, monopolies, offices, tithes, coinage, hearth-money, and excise taxes.

Petty begins by outlining the broad purposes of public charges—defense, governance, justice, clergy, education, welfare, and infrastructure—and identifies factors that inflate these burdens, such as reluctance to pay taxes, scarcity of coin, and the costs of war. He presents a pragmatic tone, acknowledging the complexity of reform and the likelihood that his proposals may be overlooked, yet he persistently advocates for efficiency, fairness, and social responsibility.

A significant portion of the treatise critiques existing institutions. Petty calls for reducing the number of parishes and clergy to save public expenses, arguing that modestly educated curates could serve multiple chapels effectively. He suggests reforming church revenues and clergy celibacy to improve efficiency and reduce costs. Similarly, he proposes abolishing superfluous government offices and reducing fees to lessen the public charge. Universities and professional bodies are also targeted for downsizing to cut expenses.

The treatise explores taxation methods in detail. Petty analyzes land taxes, showing how they function like consumption taxes affecting landlords, tenants, and consumers. He warns against housing taxes that discourage new building, leading to urban decay. He advocates for excise taxes on commodities near consumption, highlighting hearth-money as a particularly fair and efficient form. The discussion includes the economic consequences of raising or debasing coinage, emphasizing the disproportionate impact on laborers and the poor.

Trade and money flow receive careful attention. Petty critiques customs duties as outdated and prone to smuggling and bribery, proposing their replacement with tonnage duties on ships or insurance premiums to cover maritime risks. He reflects on the impracticality of prohibiting money export, noting its effects on merchants’ bargaining power and the economy. The treatise also touches on the decline of English cloth manufacture due to Dutch competition and suggests learning from Dutch manufacturing techniques.

Social concerns permeate the work. Petty shows sympathy for the poor and unemployed, advocating public works like road building and mining to provide employment and reduce crime. He stresses the importance of proportional and fair taxation to maintain social stability and warns of the dangers of religious persecution and social inequalities as causes of civil unrest.

Throughout, Petty employs economic principles grounded in labor and natural productivity, proposing that all values be measured by land and labor. He calls for detailed land surveys to improve rent assessments and tax fairness. His tone is analytical and reform-minded, occasionally ironic, and always pragmatic. He balances critique of existing structures with cautious proposals to avoid social harm.

The treatise’s language reflects its 17th-century origins, with some Latin and Greek terms, and includes references to biblical and historical laws. While some proposals’ feasibility and long-term effects remain uncertain, the work offers a rich, systematic exploration of taxation, governance, and economic policy, especially as they relate to Ireland’s condition in Petty’s time.