The consensus on climate change is the effect of free speech as John Stuart Mill theorised it, it is not a threat to free speech as George Brandis so wrongly argues, writes Henry Martyn Lloyd.

"I'm a John Stuart Mill man," says Senator George Brandis in a recent interview with Spiked magazine. Mill would be turning in his grave.

In the interview Brandis dwells at length on the famous chapter two of Mill's 1859 On Liberty. The chapter is one of the most articulate and persuasive arguments in favour of the liberty of thought and expression in the tradition.

Senator Brandis is correct in saying that for Mill "the best way for the public to be enlightened, for wicked opinions to be exposed for what they are, is to get them out in the cold light of day and let there be a contest of ideas." That Brandis has nonetheless misunderstood the chapter is made clear by his attempt to apply Mill's argument to two recent examples, the "Andrew Bolt case" and the question of climate change.

He particularly signals out as a threat to freedom of speech Senator Penny Wong, who he scathingly characterises as the "high priestess of political correctness", and her statement that climate change "science is settled".

Mill's chapter is worth re-reading and Senator Brandis would benefit from doing so. It is not based on the idea of the absolute rights of the individual. Rather, it is based on a careful consideration of the procedures for arriving at truth given human fallibility. The truth-seeker can never completely eliminate the possibility that they may be in error but they are capable of rectifying their error through experience and particularly through discussion with those who oppose their views.

This leads to a powerful argument against censorship.

When Mill criticised dogmatic ways of knowing he particularly had in mind religious believers who refused to engage with "heretics" because they presupposed their error. When he criticised those who based their knowledge on authority he had in mind those who simply accepted received religious dogma without understanding it.

Mill's argument was not just applicable to religious belief. He advocated a community of open inquiry where the truth-seeker could be sure their beliefs were sound because they had survived in open discussion with others. This was a precursor to contemporary practices of science and Mill was a significant theorist of natural philosophy, as science was then called. This procedure has developed into a contemporary practice where scientists scrutinise each other's ideas largely though the process of publishing peer-reviewed journal articles.

By the mid-19th century the professionalisation of the sciences was only beginning to intensify. Mill could still conceive of an educated citizen having a good understanding of most topics within natural philosophy. By the beginning of the 21st century human knowledge, and, in particularly science, is now far too large and fields too specialised for this to still be the case. This does not mean that relying on the knowledge of scientists in a discipline we don't fully understand is dogmatic knowing in the sense Mill criticised. Rather, it shows a sound recognition of the limits and fallibility of our knowledge.

Mill advocates that we consider views that oppose ours deliberately, carefully, and from the point of view of the person who is presenting them. This consideration need not continue forever but only for as long as "is just". Once we have done this there is of course no requirement that we agree with that view.

Error remains error. Further, there is no requirement that we continue to discuss the matter until our opponent agrees with us. Mill recognised that many "heretics" were either too obstinate, or ill-informed, or more importantly for us, too corrupted by vested interests, to change their erroneous views. It is less important that the other change their erroneous views, than that we change ours if we are the one in error.

Senator Brandis fails to realise this.

Brandis finds "deplorable" the way "one side [has] the orthodoxy on its side and delegitimises the views of those who disagree, rather than engaging with them intellectually and showing them why they are wrong." Brandis describes how Senator Wong would "stand up in the Senate and say 'The science is settled'. In other words, 'I am not even going to engage in a debate with you'. It was ignorant, it was medieval, the approach of these true believers in climate change."

Brandis seems to think that it is necessary that debate continue until those in error come to accept their error. Mill had no such requirement and nor should he.

For Mill there is nothing in principle that prevents the forming of a consensus view on any matter, scientific, religious, or political. In fact, Mill held that the ideal of knowledge is true consensus. Ensuring liberty of thought and discussion does not prevent consensus, rather the opposite, the ideal of discussion is convergence on truth even though this convergence will always be incomplete and must never become dogmatic.

There will always be "flat earthers". Yet Mill maintained a sense of optimism about the progress of human knowledge holding that the number of undisputed doctrines will constantly increase and that human wellbeing could be measured by the "number and gravity of the truths" that have reached this point.

Looking back on the 150 years since this was written we can say that consensus has not been forthcoming on matters of theology but that it has been forthcoming on a great many scientific questions. We can certainly agree that the wellbeing of humankind has benefited accordingly.

Mill held that the great advantage of truth is that although it may be suppressed many times it will eventually be rediscovered and will rise to withstand all subsequent attempts to suppress it. Those warning of the dangers of climate change were among the "heretics". The view has gradually prevailed and Senator Wong is right to now say "the science is in". Increasingly there is community consensus and we may hope soon political consensus. This consensus is the effect of free speech as Mill theorised it, it is not a threat to free speech as Brandis so wrongly argues.

Brandis invokes the idea of a new and "illiberal climate of anti-intellectualism" that "would deny the legitimacy of an alternative point of view, where rather than winning the argument [they] exclude their antagonists from the argument."

If Brandis thinks there is a cultural consensus that can be described as a "tyranny of political correctness" he needs to argue his case. He deserves to be listened to and for his argument to be carefully considered. But because there is no problem with consensus in itself he needs to show not just that there is a consensus but that the consensus is in error.

"Heterodox" views ought not to be censored and they deserve careful consideration but they need to be true to gain legitimacy.

Henry Martyn Lloyd is a lecturer in the History of Philosophy at the University of Queensland. View his full profile here.