In argumentation, we can find fallacies. What are they? Fallacies are defined as arguments that are “apparently correct in form, but actually invalid”. It is important to know fallacies and be able to identify them. So we shall now go through some examples. Let us start with the “appeal to ignorance”, in the sense of “lack of evidence”. “Mom didn’t say I couldn’t take her car, so I thought it was ok and I took it”. The underlying reasoning is “if a proposition has not been disproven, then it cannot be considered false, and must therefore be considered true.” Once the reasoning is unfolded, as you can see, the invalidity stands out, but nonetheless this argument is widely used and people actually believe it. I would like to add here that some of its uses are actually not bad – not at all! They make things safer actually. It is based on an argument of ignorance that someone is considered innocent until proven guilty. It may be faulty from a logical point of view, but it works fine, according to me, from an ethical point of view. A quite clever fallacy that is often used is the “straw man” fallacy. It consists into deliberately modifying the interlocutor’s thesis turning it, let's say, from A to B and then into answering to B instead of to A. This happens if A is “too hard a bite” and if B is similar enough to A to deceive the addressee and the audience. If the supporter of A is not smart enough, the discussion moves from A to B without her noticing. And she may end up defeated. Let us see an example: “I’m actually in favor of renewable sources. I think they can contribute to a nation’s energy demand.” “Oh, but if we were to use renewable sources only, we could not do all the things that we do now, they are not constant and moreover they don’t generate enough energy!” As it can be seen, the position of the first interlocutor has been skillfully modified: from “renewables sources COULD CONTRIBUTE…” to “renewables sources should be the ONLY source of energy”. And this second position is much easier to refute than the first. For my third example of fallacy, I will use a speech from a movie that I like very much: Braveheart. In the story, the hero, William Wallace, prompts a bunch of poorly equipped Scottish patriots to fight against a whole army of well-equipped English soldiers using the argument of “irreparable direction”. Here is what Wallace says: “…Aye, fight and you may die. Run and you'll live - at least a while. And dying in your beds many years from now, would you be willing to trade all the days, from this day to that, for one chance, just one chance, to come back here and tell our enemies that they may take our lives, but they'll never take our freedom…” What Wallace is doing is showing the remote consequences of his fellowmen’s choice of not fighting and telling them: “It’s now or never, if you don’t fight now, you will regret it all your life”. This kind of argument is quite powerful: any “now or never” move is going to make an impression, for sure. The fallacy lies in the fact that being the last option does not mean that that option is good, advisable, appropriate… At least, not necessarily. But if you use it, you will see your addressee falter. Eventually, the fallacy of the argument from authority. It takes place when we use an authority to support a claim. When the appeal is made to a false authority, then the invalidity is evident. But even if the authority is valid, still the argument is a fallacy. Why? Because the mere fact that the authority X says that Y is true is not enough per se to conclude that Y is true. Concerning this fallacy, first of all it must be noted that it is more about claims than about facts, otherwise we would stop giving lectures! Second, I have to warn you: do not think that from now on you cannot make reference to any authority, because it would not be correct. Rather, I strongly suggest you to make reference to authorities to support claims, as we do all the time in scientific research. If you are discussing the general theory of relativity, it is definitely a good idea to bring in Einstein as an authority to support a claim. But you must be aware that even if you use Einstein as an authority, someone may object your point, based on data, figures, facts, evidences... And she may be right. And in that case, you must be ready to admit it. I want to finish up with a personal opinion: I think that in human life, there are many shades of grey (probably more than 50). Some fallacies are more harmful than others; some fallacies can be acceptable, as long as we acknowledge their limitations. As seen with the argument from authority, fallacies are errors in reasoning, not evil weapons, at least not all the times and not in all their possible uses. So it is important to know them: to put them to good use, while being aware of their weaknesses, or to be able to identify them when they are used against you and be ready to react.