Rio Grande do Sul is a place with a tradition of fierce polemics and divisions. This reflects the very low communication capacity of its people and should be no point of pride. These controversies have expanded even into scientific and technical aspects, such as the discussion over whether the Guaíba is a river or a lake.

In this case, I hold the opinion that it is a lake.

But before bringing more consistent points regarding this, I find it necessary to prepare the ground by reviewing how not to argue about the Guaíba.

Read also: How to argue about the Guaíba

Fallacies and biases

A legitimate argument in favor of a given geographical nomenclature for the Guaíba must be anchored in the foundations of physical geography.

Any proposition that departs from a geophysical basis is not a rational argument, but a subjective desire. This seems obvious, but the discussion surrounding the Guaíba is overtaken by fallacies and biases, summarized below.

Pure spite

One of the most present fallacies in this discussion, though not always admitted in public, is the argument against the person, or argumentum ad hominem. This fallacy seeks to assert that the Guaíba is a river out of pure spite for the most famous proponent of the lake classification, Professor Rualdo Menegat. The fallacy can be summarized by the following reasoning:

“So-and-so says the Guaíba is a lake. But I don’t like So-and-so. Therefore, he must be wrong and the Guaíba is a river!”

They said it, so it’s final

The appeal to authority, or argumentum ad verecundiam, is also common in this plot. This fallacy is the opposite of the ad hominem, as it occurs when the credentials of the proponents are used as if they were sufficient to close the matter. This fallacy can occur on both sides, but we have seen more “pulling rank” in the case of the river, such as when the IBGE defined the Guaíba as a river on a map without much explanation.

“The renowned institution X states that the Guaíba is a river (or lake, etc.). Therefore, the Guaíba is a river (or lake, etc.)!”

The people decide

Another fallacy wandering through the corridors is the so-called appeal to custom, or argumentum ad populum and its variants, which are disguised forms of conservatism. In this case, the proposition seeks to claim that the Guaíba is a river simply because the majority of the population prefers to call it that. One hybridization with the appeal to authority is appealing to historical nomenclature, such as pointing to old maps and nautical charts that name the Guaíba as a river.

“Since the beginning, it has been said that the Guaíba is a river. So the Guaíba can only be a river!”

For enemies, the law

The reversal of cause and effect is by far the most powerful fallacy regarding the Guaíba. In particular, it merges with a confirmation bias that makes citizens defend that the Guaíba is a river because of its legal implications under the Forest Code. The reasoning is as follows:

“The Guaíba waterfront must be public, free from the advances of real estate speculation! The legal protection of riverbanks is more restrictive than the legal protection for lakes. Therefore, the Guaíba can only be a river, as this guarantees more protection for the banks.”

How would opinion stand in this case if the law were suddenly reversed, and the lake now guaranteed more protection? Would the opinion change to lake?

Don’t get me wrong. I believe the waterfront should be 100% public so that the Guaíba can be enjoyed democratically. But wanting that does not automatically imply classifying the Guaíba as a river.

All at the same time

Once, in a debate promoted by the IAB (Institute of Architects of Brazil), I witnessed a gentleman defend the “Guaíba River” thesis using all these fallacies at once, at a clearly schizophrenic level.

On that occasion, the spite toward Prof. Menegat escalated into public defamation, culminating in a grand conspiracy theory where real estate speculation was supposedly the true force behind the lake classification—as if no technical argument to that effect existed.

With what I have organized here, I hope we now have the means to move toward something more sober.