Drinking Age.

"The comparisons used where X and Y are variables does not apply because anything can be replaced in terms of X." That's how logic works, from general to specific you establish the form and rule of correct inference and then you apply it to one case. "The difference between alcohol and pot is that alcohol is legal in all states where pot is not." Again, not if you're 18. If I added a third criteria 'and is currently legal' then alcohol at 18 wouldn't get you your conclusion. "This argument does not apply to drugs in any sense because they are illegal" If you're argument doesn't apply to illegal things then it can't apply to drinking at 18 since that is illegal. "18 you are allowed many rights including the right to own a gun which is a possible." It is plausible that on average a gun in the hands of a sober 18 year old is safer than a gun in the hands of a drunk 21 year old. "Existing Legality can be used because we are not arguing if alcohol should be legal, but instead who it should be legal to." Who it should be legal to is a subset of whether it should be legal. Saying it should be legal is saying it should be legal to someone at least. In order to know why it should be legal for 18 year olds you must show why it should be legal for 21 year olds and illustrate why those criteria are also met for 18 year olds. The criteria you have given so far for why it should be legal for 18 year olds do not constrain the application to alcohol. "21 is an arbitrary number in that it is a random number" So is 18, nature does not have a pop-thermometer in people that goes "oooOK this one’s done." You argue that 18 is the age of legal responsibility but that age is just as arbitrary as 21. "Do you think it is consistent to say that 18 year olds are adult enough to have the responsibility of serving in the army and owning a gun but are not adult enough to drink alcohol?" The law gives not justification (nor do any laws). The reasons people think they are good or bad are legion. If the law was meant to pick an arbitrary date for a minimum 'adultness' required to drink it wouldn't being consistent. However there are a lot of people who think of the law in terms of 'social goals' they don't care if it's justified in terms of rights and responsibilities duly owed an individual. To them a three year period of becoming familiar with those rights and responsibilities could be 'training' for more rights and responsibilities. They might say "they need to understand the importance of their legal culpability sober before they can be given the opportunity to risk that culpability by impairing their judgment." That is why it was very important for you to set out the principles of judging a law in your argument. "Show me why it would be consistent." Consistency and inconsistency are undefined without the context of underlying reasons. For instance you set some water to boil, and then you pour a lot of salt in it. Whether these two actions are consistent depends on the reasons. If you want boiling water for tea then it is inconsistent to make it overly salty. If you are trying to cook pasta on the other hand they are consistent. I tried to ask you what your reasons to make laws about alcohol consumption would be (the whole scope not just for a specific age) so we could evaluate whether it was consistent to make it legal at 21 and illegal at 18 but all you gave me are those two above and I had to parse them out myself. Given those criteria (1 and 2) it is inconsistent to make alcohol illegal for 21 and legal for 18. However it is also inconsistent to make alcohol legal but not pot. Readers can decide if they accept those criteria and their implications I suppose. (Although if past experience is any guide RFD's will have nothing to do with any of this).