This is a fallacy, which takes place in case when the expression, which is taken in conditional, comparative sense, is taken then after in absolute sense, like absolute proof. For example, in a newspaper (Aggiornamenti Sociali) was an article, where a person wrote about the characteristics of different poisons. There he wrote that arsenic and strychnine in big quantities in case there are inside of human's body, will cause death. We talk here about those poisons in conditional sense, it means we tell about their poison in case there are in the human's body in big quantities. But he writes that they always cause death as well. Here we have our fallacy A dicto secundum quid ad dictum simpliciter - because we know that they don't cause death in small quantities, and as far as we know, in very small quantities they can be used as medicines.
I've read a questionnaire (Questionnaire "Health and the City",), where a sociologist want to ask people several questions regarding improvement of medical and other institutions in the city. There he tried to combine in one concept two different, which are quite close by content and to form another, new concept. There was a question:
"Please tell, what do you think, we have to change in the work of medical and sanitary institutions in our city?"
Here the sociologist tries to combine two things, which are quite close by the content, like "medical" and "sanitary" institutions - in one common concept "institutions which are aware of people's health".
The peculiarities of such questions are that a positive answer (the same as negative) for any of those two questions, or the answer, which differs by content for any of two combined questions, can be used as the answer for both questions.
The advantage of such questions is that they allow having more information, for example, not only information regarding the improvement of medical institutions or sanitary institutions in the city, but in common, for all complexes of institutions which are aware of people's health.
In one newspaper (Corriere Adriatico (Ancona)) where was an article specialized in debates on physics was one discussion. One person wanted to prove thesis "All particles of matter have one and the same weight". He answered the question, where his opponent wanted to know the true position, why does he thinks so, he gave the following answer: "In case we'll take two substances with a similar volume and size, we'll find that the substance which has weight more, has more particles, it means, that the greater weight depends on exactly the quantity of particles". The other question to him, where they asked, from where he knows that the greater weight of the substance with similar volume and size depends exactly on the quantity of particles, he answered: "In case we'll take into consideration that all particles of the matter have the same weight, it is going without saying that the more weight has the substance, the bigger quantity of particles is has in case of similar volume and size".
In this example the thesis is proved with the help of position which can be proved in case we allow the thesis is true. So, here we find a fallacy petition principlii, where we find as true the position which has to be proven.
Here a person proves or disproves another thesis, which wasn't adduced from the very beginning. It can be used in two ways: the first is used when a person proves not all theses, so some part of thesis is left not proved and another way when the person proves too much, so from all information there is not only thesis itself, but some false one as well. For example, let's take one talk-show (Talk-show The Tonight Hour), where a person wanted to prove if it is correct or not to end life with suicide. The basis for his arguments was a fact that a person cannot bereave himself the things he didn't give to himself. He tried to prove too much, because we can make conclusion from his proof that he cannot cut his nails, for example, he cannot sell the things he inherited from somebody or somebody gave to him as a present, etc. We tell this because all those things are given to him not by himself, as well. It means, his physical characteristics, and the things in the worlds, he didn't owe. So, we can tell that he didn't prove the thesis.