According to the eminent historian J. B. Bury, the idea of human progress “is based on an interpretation of history which regards men as slowly advancing … in a definite and desirable direction, and infers that this progress will continue indefinitely.” Bury contends that progress, in this sense, is a distinctively modern notion—one that does not begin to take shape until the 16th and 17th centuries, whereas other historians, such as Robert Nisbet, attribute the idea to Greek, Roman, and Christian writers long before the advent of the modern era.

A libertarian theory of progress is one that stresses the role of liberty in the progressive improvement of humankind. Whatever position we may take in the historical controversies about the origin of the idea of progress and its relationship to other ideas (such as the belief in an Arcadian golden age, original sin, and divine providence), there can be little doubt that the link between individual freedom and progress was forged by post-Renaissance philosophers, historians, economists, and social theorists.

In The Idea of Progress, Bury divides modern theories of progress into two types, which he characterizes as socialist and liberal. The socialist version he describes as “a symmetrical system in which the authority of the state is preponderant, and the individual has little more value than a cog in a well-oiled wheel: his place is assigned; it is not his right to go his own way.” Liberalism, in contrast, views individual freedom and social diversity as essential to progress. Unlike the closed system of socialism, in which the ultimate goal of progress is foreseeable, having been mapped out in advance by central planners, classical liberalism was historically affiliated with a theory known as “indefinite progress.” In this approach, no limits can be set to progress, nor can we predict the exact path or form that progress will take. “Individual liberty is the motive force” of indefinite progress, and this decentralized, spontaneous process generates rapid innovations that cannot be predicted or controlled by any individual, group, or institution, including government.

Theories of progress are typically concerned with three spheres of human activity: intellectual, moral, and economic.

Libertarian theories of intellectual progress emerged during the 17th century, as John Milton, Benedict Spinoza, and John Locke, among others, argued that freedom of thought, discussion, and publication are essential to the advancement of knowledge. Often grouped under the collective label of “liberty of conscience,” these freedoms came to be widely accepted as indispensable to the pursuit of truth in religion, science, and other spheres, and they played a crucial role in the struggle for religious toleration.

We do not find this near-unanimity, even among libertarian thinkers, on the subject of moral progress. It has often been pointed out that knowledge can be used for good or evil purposes, and some liberals, such as Adam Ferguson and Joseph Priestley, warned against the enervating effects of luxury and other vices, which they believed would lead to the corruption of those moral virtues necessary to sustain a free society. Other liberals disagreed. In the writings of David Hume, Edward Gibbon, Adam Smith, and others, we see various arguments in defense of luxury and other personal vices (i.e., those that do not violate the rights of others) based largely on their unintended, but beneficial, consequences to society as a whole. Many of these arguments are variations on a theme first presented by the Dutch philosopher Bernard Mandeville in his notorious book, The Fable of the Bees: Or, Private Vices, Publick Benefits, first published in 1705 as The Grumbling Hiveand greatly expanded in subsequent editions.

Another internal debate among classical liberals addressed the possibility of moral progress, a topic that received a good deal of attention during the 19th century. W. E. H. Lecky, J. S. Mill, Herbert Spencer, and many other liberals maintained that progress in the moral sphere (especially the “sentiment of justice”) is as evident in the historical record as any other kind of progress, and they point to advances in religious toleration, the repudiation of torture, and the abolition of slavery to buttress their case. But other liberals, most notably H. T. Buckle and others influenced by the positivistic sociology of Auguste Comte, presented a different analysis.

In the first volume of his best-selling Introduction to the History of Civilization in England (1857), Buckle defends the thesis that moral sentiments and motives, unlike knowledge, are “stationary” and do not progress from one generation to the next. As Buckle put it, “the sole essentials of morals … have been known for thousands of years, and not one jot or tittle has been added to them by all the sermons, homilies, and text-books which moralists and theologians have been able to produce.” True progress occurs in the realm of knowledge as people become more cognizant of the long-range consequences of their decisions and actions.

Perhaps the most important contribution of libertarian thinkers was in the sphere of economic progress. The growth of commerce, or what was sometimes called the commercial spirit, was widely regarded by liberals as a lynchpin of socioeconomic progress.

In Book III of The Wealth of Nations, Adam Smith discusses “the natural progress of opulence.” The motive of self-interest, when confined within the sphere of justice, naturally leads to a division of labor that is “advantageous to all the different persons employed in the various occupations.” This natural economic order—which develops spontaneously, without foresight or central planning—is called natural because it is “promoted by the natural inclinations of men” in a “system of natural liberty,” in which the equal rights of every individual to life, liberty, and property are secured by a just system of law and government.

Free-market liberals agreed with Montesquieu that the “natural effect of commerce is to lead to peace” because trade creates a mutual dependence among nations, and “all unions are founded on mutual needs.” Progress, in this view, is best achieved during periods of peace.

Although many liberals—such as the physiocrats Turgot, David Hume, and Adam Smith in the 18th century and H. T. Buckle, Frédéric Bastiat, Richard Cobden, and John Bright in the 19th century—emphasized the connection between free trade and peace and the resulting progress these made possible, the most systematic exposition of this theme appears in the voluminous writings of Herbert Spencer. Elaborating on a distinction made by H. S. Maine between societies based on status as opposed to those based on contract, Spencer dubbed two basic types of social organization militant and industrial.

According to Spencer, it is primarily due to the growth of commerce that the despotism and “compulsory cooperation” of a militant social structure evolve into the individual freedom and “voluntary cooperation” that characterize industrial society. The contractual relationships of commerce, “in which the mutual rendering of services is unforced and neither individual subordinated becomes the predominant relationship throughout society,” as its perceived benefits are extended to other forms of social relationships. “Right of private judgment in religious matters gradually establishes itself along with the establishment of political rights,” and coercive uniformity gives place to “a varied non-conformity maintained by willing union.” Hence, the growth of commerce naturally tends to generate progress “through stages of increasing freedom,” and this progress is accompanied by an ideological development of “sentiments and ideas,” such as the principles of individual rights and limited government. Certainly if mankind’s progress is causally related to the extension of individual liberty, there is less reason today to believe that this progress is, over the long term, inevitable. There appears no reason to accept the view that individual autonomy will inexorably flourish and expand and that the free and peaceful interactions among people will play an increasingly greater role in social life. Indeed, given the history of the 20th century, there is ample evidence to point to the fragility of free and peaceful societies.