Why, according to Marx, do revolutions happen, and is his explanation adequate?

Marx never produced a precise account of how revolutions occur, nor how the predicted communist revolution would take place. Instead, his ideas must be built up based on his writings on the revolutions that were taking place around him at the time of his writing or had done so in the recent past. His points of reference were the English Revolution of 1640-88, the French Revolution of 1789, and the German Revolution of 1848. These revolutions were bourgeois revolutions, a transition from absolute to constitutional monarchies with a republican interval included. The feudal society became a capitalist one. At the same time that these revolutions took place, Marx believed that Communist parties would be formed which would wait for the correct time for the communist revolution would take place, where there would be transition from a capitalist society to a communist one.
For Marx, there were three main flaws of capitalism that would ultimately lead to a proletariat revolution and movement to a communist society; these were alienation, exploitation, and inefficiency.
Alienation was the most important of these for Marx, because he believed that communism would remove it completely. By alienation is meant the alienation of man from achieving his human possibilities through his own activity. Marx believed that the good life was concerned with active self-realisation; capitalism frustrated human development, and prevented people from realising their potential as all-round creators. Capitalism offers this opportunity to the few, but denies it to the majority. Under communism, every individual will lead a rich and active life. As Marx put it, people will be able to "hunt in the morning, fish in the afternoon, rear cattle in the evening, and be critical critics after dinner." This is not to say that everyone will lead a life of leisure and that inefficiency will grow. On the contrary, the problem of efficiency will automatically be solved with this active self-realisation, as it will also be applied to the world of work through scientific and technical work that will raise productivity far beyond anything seen under capitalism. Furthermore, the alienation that occurs in the worker as a result of the exploitation of labour by the capitalist would, of course, cease to exist in a communist society, as there would be no exploitation with the means of production in common ownership.
Exploitation will provide the motivation for revolt, protest, riot, or revolution. According to Marx, a person is exploited if he or she performs more labour than is necessary to produce the goods they consume. There exist in tandem with the exploited the exploiters, those who work fewer hours than are necessary to produce the goods they consume. Labourers are exploited because they are forced to sell their labour power to capitalists - they have no land to cultivate, nor the capital necessary to set themselves up in business. They do not have the entrepreneurial skill to persuade a bank to lend them money to set up a business, and the other alternatives to wage labour (begging, stealing, starving, etc.) are so unattractive that no-one would choose them. Hence the choice of wage-labour is forced upon them, if not coerced. This exploitation leads to the emergence of class divisions between the capital-owning bourgeoisie, and the proletariat wage-labourers.
Marx believed that under communism, there would be less inefficiency than in capitalism. The communist revolution would take place when and because communist relations of production became optimal for the development of the productive forces. What does this mean? The productive forces are anything and everything that promotes the mastery of man over nature for the purpose of want satisfaction. The most important of these are technology, science, and human skills. The development of the productive forces measures the degree to which the same goods can be produced with less human labour. Relations of production are approximately equivalent to property rights. Under capitalism, productive forces develop at an ever faster rate. However, at some level of their development, communist relations of production will allow for an even higher rate of their production. Hence the communist revolution will not be caused by technical stagnation, but by the prospect of unprecedented technical expansion.
The combination of these three evils would, according to Marx, lead to a proletariat revolution that would seize power and transform society into a communist one. This prompts questions about how one should go about achieving this revolution; by overt or covert means, with or without the use of violence, and what would be the relationship between the working class organising the revolution and the existing political institutions. The combinations of possible answers to these questions lie between the two extremes of a secret conspiracy plotting the violent overthrow of the existing system, and a peaceful transition using the capitalist state to transform the system from within. Marx did not hold either of these views, but it is difficult to ascertain which of the multitude of intermediate positions he did occupy. It seems, though, that using the existing political institutions would be nearly impossible without the introduction of universal suffrage; without this, the workers could not achieve office and set about transforming the state from the inside. It follows from this denial of voting rights that Marx may not have been entirely hostile to the use of violence, as it could well have been the only tool available to the workers.
However, there are objections to the notion that the features Marx identifies as the downsides of capitalism will inevitably lead to revolutionary tendencies among those on the receiving end of these. Alienation may not provide much motivation for a change to communism if the worker does not know what he is missing out on. To understand and rationally desire the self-realisation that communism will bring to everyone requires experience of both capitalism and communism, but as we have already noted, it is only the minority in capitalism that have experienced both, and those that are benefiting under capitalism will see no reason to change to a communist society. Although they may accept the promise that communism will be more technically efficient, and thus desire it as a means to increased consumption, why should they believe it when the technical efficiency is supposed to follow the movement away from consumption towards the active creation of self-realisation of communism? This would seem to be a hard paradox for the majority of workers to accept, despite Marx's insistence that they would educate themselves prior to the revolution. In other words, the promise of increased output and efficiency in a communist society seems remote and uncertain; in response to being told "You don't know what you're missing," the workers are likely to reply "Then how do you expect us to miss it?" The workers are likely to be myopic, more interested in their own welfare than securing a better future for their descendants.
This uncertainty also means that claim of capitalism being inefficient will also not be enough to incite a worker's revolt, provided that most see the current situation as "satisfactory." This is because in a choice between a satisfactory current situation and a hypothetically superior alternative, people will generally choose the former for two reasons. Firstly, there will be uncertainty, as I have already mentioned. Despite the communists' theories, without evidence pointing to the guaranteed superiority of the communist system, their arguments will be treated with a certain amount of scepticism. Secondly, there are costs associated in a revolution that could become violent and involve sacrificing themselves and their families for the sake of future generations. Most people in this situation would be content to live out their lives under capitalist conditions, where they can be guaranteed a reasonably good life. Thus the only time when the inefficiency of capital will provide a serious motivating power is when there is absolute misery and poverty among the working class, so the workers have nothing to lose by revolting.
Also related to this point is the necessary assumption in Marx's theories that the ruling classes in capitalism are irrational. If not, then the development of the productive forces in capitalism should increase everyone's standard of living through some sort of "trickle-down" effect. This would dampen any reactionary tendencies among the working class, especially if it helped to guard against unemployment. The development of the productive forces would only give rise to revolutionary tendencies if the benefits of capitalism were badly distributed, and in an inciteful way. However, Marx failed to provide any arguments for irrationality on the part of the ruling classes.
Finally, it is implausible that the time at which communism becomes a better framework for the development of the productive forces corresponds with the optimal time period to launch a revolution, i.e. a time when the ills of capitalism become so great that the motivation for a revolution becomes an unstoppable force. As we have already seen, Marx believed that economic stagnation would not be the cause of a revolution, but only a stagnation or prolonged recession will give rise to the absolute poverty among the working classes that would facilitate a revolution. Marx is trapped in a vicious circle here. Empirical evidence shows that the countries in which communist revolutions have occurred have not been in a position to overtake capitalism; rather, they have taken place in backward countries that were nowhere near the stage of development at which they could overtake capitalism. Marx would claim that this is due to premature revolution, and that given enough time these countries might eventually overtake capitalism. However, empirical comparisons of communist countries and capitalist ones suggest that this is unlikely to happen in the foreseeable future, if at all.

Marx never produced a precise account of how revolutions occur, nor how the predicted communist revolution would take place. Instead, his ideas must be built up based on his writings on the revolutions that were taking place around him at the time of his writing or had done so in the recent past. His points of reference were the English Revolution of 1640-88, the French Revolution of 1789, and the German Revolution of 1848. These revolutions were bourgeois revolutions, a transition from absolute to constitutional monarchies with a republican interval included. The feudal society became a capitalist one. At the same time that these revolutions took place, Marx believed that Communist parties would be formed which would wait for the correct time for the communist revolution would take place, where there would be transition from a capitalist society to a communist one. For Marx, there were three main flaws of capitalism that would ultimately lead to a proletariat revolution and movement to a communist society; these were alienation, exploitation, and inefficiency. Alienation was the most important of these for Marx, because he believed that communism would remove it completely. By alienation is meant the alienation of man from achieving his human possibilities through his own activity. Marx believed that the good life was concerned with active self-realisation; capitalism frustrated human development, and prevented people from realising their potential as all-round creators. Capitalism offers this opportunity to the few, but denies it to the majority. Under communism, every individual will lead a rich and active life. As Marx put it, people will be able to "hunt in the morning, fish in the afternoon, rear cattle in the evening, and be critical critics after dinner." This is not to say that everyone will lead a life of leisure and that inefficiency will grow. On the contrary, the problem of efficiency will automatically be solved with this active self-realisation, as it will also be applied to the world of work through scientific and technical work that will raise productivity far beyond anything seen under capitalism. Furthermore, the alienation that occurs in the worker as a result of the exploitation of labour by the capitalist would, of course, cease to exist in a communist society, as there would be no exploitation with the means of production in common ownership. Exploitation will provide the motivation for revolt, protest, riot, or revolution. According to Marx, a person is exploited if he or she performs more labour than is necessary to produce the goods they consume. There exist in tandem with the exploited the exploiters, those who work fewer hours than are necessary to produce the goods they consume. Labourers are exploited because they are forced to sell their labour power to capitalists - they have no land to cultivate, nor the capital necessary to set themselves up in business. They do not have the entrepreneurial skill to persuade a bank to lend them money to set up a business, and the other alternatives to wage labour (begging, stealing, starving, etc.) are so unattractive that no-one would choose them. Hence the choice of wage-labour is forced upon them, if not coerced. This exploitation leads to the emergence of class divisions between the capital-owning bourgeoisie, and the proletariat wage-labourers. Marx believed that under communism, there would be less inefficiency than in capitalism. The communist revolution would take place when and because communist relations of production became optimal for the development of the productive forces. What does this mean? The productive forces are anything and everything that promotes the mastery of man over nature for the purpose of want satisfaction. The most important of these are technology, science, and human skills. The development of the productive forces measures the degree to which the same goods can be produced with less human labour. Relations of production are approximately equivalent to property rights. Under capitalism, productive forces develop at an ever faster rate. However, at some level of their development, communist relations of production will allow for an even higher rate of their production. Hence the communist revolution will not be caused by technical stagnation, but by the prospect of unprecedented technical expansion. The combination of these three evils would, according to Marx, lead to a proletariat revolution that would seize power and transform society into a communist one. This prompts questions about how one should go about achieving this revolution; by overt or covert means, with or without the use of violence, and what would be the relationship between the working class organising the revolution and the existing political institutions. The combinations of possible answers to these questions lie between the two extremes of a secret conspiracy plotting the violent overthrow of the existing system, and a peaceful transition using the capitalist state to transform the system from within. Marx did not hold either of these views, but it is difficult to ascertain which of the multitude of intermediate positions he did occupy. It seems, though, that using the existing political institutions would be nearly impossible without the introduction of universal suffrage; without this, the workers could not achieve office and set about transforming the state from the inside. It follows from this denial of voting rights that Marx may not have been entirely hostile to the use of violence, as it could well have been the only tool available to the workers. However, there are objections to the notion that the features Marx identifies as the downsides of capitalism will inevitably lead to revolutionary tendencies among those on the receiving end of these. Alienation may not provide much motivation for a change to communism if the worker does not know what he is missing out on. To understand and rationally desire the self-realisation that communism will bring to everyone requires experience of both capitalism and communism, but as we have already noted, it is only the minority in capitalism that have experienced both, and those that are benefiting under capitalism will see no reason to change to a communist society. Although they may accept the promise that communism will be more technically efficient, and thus desire it as a means to increased consumption, why should they believe it when the technical efficiency is supposed to follow the movement away from consumption towards the active creation of self-realisation of communism? This would seem to be a hard paradox for the majority of workers to accept, despite Marx's insistence that they would educate themselves prior to the revolution. In other words, the promise of increased output and efficiency in a communist society seems remote and uncertain; in response to being told "You don't know what you're missing," the workers are likely to reply "Then how do you expect us to miss it?" The workers are likely to be myopic, more interested in their own welfare than securing a better future for their descendants. This uncertainty also means that claim of capitalism being inefficient will also not be enough to incite a worker's revolt, provided that most see the current situation as "satisfactory." This is because in a choice between a satisfactory current situation and a hypothetically superior alternative, people will generally choose the former for two reasons. Firstly, there will be uncertainty, as I have already mentioned. Despite the communists' theories, without evidence pointing to the guaranteed superiority of the communist system, their arguments will be treated with a certain amount of scepticism. Secondly, there are costs associated in a revolution that could become violent and involve sacrificing themselves and their families for the sake of future generations. Most people in this situation would be content to live out their lives under capitalist conditions, where they can be guaranteed a reasonably good life. Thus the only time when the inefficiency of capital will provide a serious motivating power is when there is absolute misery and poverty among the working class, so the workers have nothing to lose by revolting. Also related to this point is the necessary assumption in Marx's theories that the ruling classes in capitalism are irrational. If not, then the development of the productive forces in capitalism should increase everyone's standard of living through some sort of "trickle-down" effect. This would dampen any reactionary tendencies among the working class, especially if it helped to guard against unemployment. The development of the productive forces would only give rise to revolutionary tendencies if the benefits of capitalism were badly distributed, and in an inciteful way. However, Marx failed to provide any arguments for irrationality on the part of the ruling classes. Finally, it is implausible that the time at which communism becomes a better framework for the development of the productive forces corresponds with the optimal time period to launch a revolution, i.e. a time when the ills of capitalism become so great that the motivation for a revolution becomes an unstoppable force. As we have already seen, Marx believed that economic stagnation would not be the cause of a revolution, but only a stagnation or prolonged recession will give rise to the absolute poverty among the working classes that would facilitate a revolution. Marx is trapped in a vicious circle here. Empirical evidence shows that the countries in which communist revolutions have occurred have not been in a position to overtake capitalism; rather, they have taken place in backward countries that were nowhere near the stage of development at which they could overtake capitalism. Marx would claim that this is due to premature revolution, and that given enough time these countries might eventually overtake capitalism. However, empirical comparisons of communist countries and capitalist ones suggest that this is unlikely to happen in the foreseeable future, if at all.