What I Learned In School: “Valid” arguments

The new semester has begun on this, my last schedules semester as a mere old Undergraduate. This semester’s primary purpose is to fill in the two vitally important “general education” goals for my current Institute of higher learning: Art Appreciation and Philosophy.

I added a “What I Learned in School Today” category to the blog just because of this semester. My loyal readers (all 2-4 of you…) can look forward to occasional posts on other aspects of my Higher Education as the semester goes along, besides microbiology. On the metaphorical menu over the next 16 weeks: “Introduction to Philosophy” (today’s topic), “History of Western Art“, Applied Calculus, and finally I have a chance to take Environmental Chemistry.

Prior to reading some Plato for next week, we started out “Philosophy 101” with a discussion of “Valid” arguments. In Philosophy, this has a very specific meaning. If you make an argument in the general form of “This, and that, therefore something”, the argument is “valid” when if “This” and “that” are both true, then “something” must also be true.

The thing that most of the class seemed to have trouble with is that being “valid” has nothing to do with whether or not the argument is “sound“, or whether the statements in the argument are true.

An example from the class:

All mammals have lungs.
Whales have lungs.
(Therefore) all whales are mammals.

This is an invalid argument, despite the fact that every statement is actually true. The reason is simply that the fact that whales are mammals does not automatically follow from the fact that they have lungs. (Chickens have lungs, too. Does this mean chickens are mammals?…)

It took two class sessions before most of the class seemed to “get” this. I felt as though I was in Junior High again…though I think this had more to do with watching the freshman girls in front of me passing notes during the class. Come on, kids, grow up! We adults are using IM for that now! Sheesh. Kids today…

On the other hand:

You’ve got to be some kind of genius to attend college and blog at the same time.
I attend college and I blog at the same time.
I am, therefore, a genius.

is a valid argument. As written, if both of the first two statements are true, then the third statement must be true. This is where the value of valid arguments come in – if it turns out that the conclusion is false, then one of the premises must also be false. If anyone were to discover that I am, in fact, not a genius, then either it’s unnecessary to be a genius to blog and go to college at the same time, or perhaps I’m paying someone else to write this stuff for me.

Who cares, I’m a science major, not a philosophy major, right? Except: a properly designed scientific hypothesis should be a premise in a “valid argument”, and an experiment is merely a test to see if the argument is unsound. For example:

All lactic acid bacteria, grown in otherwise sterile milk, will make yogurt.(the underlying hypothesis being tested)
I inoculate sterile milk with a culture of Pediococcus damnosus(the test performed by the experiment)
(Therefore) I obtain yogurt. (Expected results and conclusion of the experiment)

This is (as far as I can tell) a completely valid argument. Now, I haven’t actually done this experiment, but let’s pretend I did, and the end result was a smelly mass that kind of looked like yogurt except it turned out to be slimy rather than firm. I cannot in fairness call it “yogurt”, so my conclusion in the argument is false. Thanks to the magic of Valid Arguments™, I know that either my assumption is wrong (maybe not all lactic acid bacteria turn sterile milk into yogurt after all), or there was a problem with the experiment (perhaps the milk was contaminated with something and wasn’t really sterile, or I grabbed a culture of something other than P.damnosus by mistake.)

Assuming I carefully recheck the materials and repeat the experiment to confirm that I really am inoculating actually-sterile milk with a definitely clean culture of P.damnosus and continue to get the same results, then my hypothesis – the first premise in the argument – must be false. I have to then go back and revise my hypothesis and test again, until I have a hypothesis that seems to consistently generate true conclusions. Thus, the “valid argument” is the basic tool which allows hypotheses to grow up and become theories.

Incidentally, some Pediococcus damnosus strains are a cause of “ropy” wine, which is why I chose that example. I don’t actually know what, if anything, it would do to pure, sterilized milk, though.

Coming up next: I picked up a 100-year-old microbiology book while on vacation!

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The Author is (currently) an autodidactic student of Industrial and Environmental microbiology, who is sick of people assuming all microbiology should be medical in nature, and who would really like to be allowed to go to graduate school one of these days now that he's finished his BS in Microbiology (with a bonus AS in Chemistry). He also enjoys exploring the Big Room (the one with the really high blue ceiling and big light that tracks from one side to the other every day) and looking at its contents from unusual mental angles.

2 thoughts on “What I Learned In School: “Valid” arguments”

  1. I finally subscribed to this blog, but I first encountered it on the ‘governmental war on science’ post, which I really enjoyed. So chalk up one success for that post.

    This is a great explanation of how science ‘ought’ to work. I tend to keep track of things like this because so many people have such a poor understanding of the process, including myself until recently. Keep up the good work! I look forward to reading what you find in this old textbook.

  2. Thanks! This poor little blog, at present, still only has a few regular readers, so I’m still in the “throwing posts out and hoping somebody likes it” stage. It’s good to know that at least one or two people think I’m doing something useful so far.

    I need to scan a few of the illustrations from the book to include with the blog post about it. I’ve been finding it both useful and fascinating to go back and see the real historical development of microbiological science. Plus, it’s nice to know that even 110 years ago, microbiologists were saying “bacteria doesn’t just mean diseases, dagnabbit!” (to paraphrase…)

    More to follow soon…now that people are starting to actually read the blog, I guess I can’t slack off so much any more.

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