Difference between SC and NC

aincao

Now, as I've been going through the exercises, I am able to identify the necessary condition and the sufficient condition for the work the majority of the time, until I get to the very convoluted passages/sentences/whatever. I have an extraordinarily tough time when it comes to PF/ Negation/ SA. I review the valid and invalid argument forms every night for two hours with flash cards trying to get it, but as of right now, I'm only able to memorize the forms. I have a hard time identifying them in practice. I feel that this has to do in part to lack of understanding the working difference between the SC and the NC. Does anyone have a way that helped them "get it", as well as any other tips for understanding Lawgic? Thanks!

aincao

Whoops, going back through my notes I finally saw the "Groups" lecture that was stuck together, guess I need to get some sleep, but any advice for understanding Lawgic and a practical definition of the difference between sufficient and necessary would be great.

sarkisp23

Glad you were able to find it! LOL but seriously I'll tell you what held me back and that was thinking about lawgic as being chronological. So "if A happens then B happens." "Happens" is not the right word. Sure, it CAN be chronological but not only chronological. Logic is about this one question: what do we know?

So, going back to NC/SC... If you have a SC, then that is enough for you to know this other thing (NC). You don't need to know any more things. It's sufficient. If you have A, then automatically you have B. The fact of having A is sufficient/enough to able to know B as a fact as well. I mean they didn't just randomly name it a sufficient condition right lol.

On the other hand, knowing a NC as a fact doesn't allow you to know the SC as a fact.

Here's an example of all this vague-ish talk: IF I drop my phone, it'll get damaged. "drop my phone" is sufficient in knowing "get damaged." But what if I hand you a damaged phone (this being the necessary condition). Can you tell me for sure the cause of the damage was a drop? Is that the only way to damage a phone? Maybe someone mistook it for a nail and hit it with a hammer. So a necessary condition doesn't say much compared to a sufficient.

I can say a million other things and I'm sure others will chime in who are geniuses at logic. But I think if you understand these concepts early on, you'll be just fine. And if you want me to elaborate on "not chronological" let me know.

aincao

Thanks, that's perfect! It makes complete sense, and now I finally have a great explanation for sufficient. I really kept struggling with that distinction when it came to logic. By not chronological are you saying that it implies, such as, for example "if i drop my phone, it'll get damaged" 'Last week I hit my phone with a hammer, and then this week I dropped it, therefore my phone was damaged this week"? I know the phrasing of that sentence isn't perfect logic or formed the best way lol.

sarkisp23

Chronological as in time-based. Or another way to think about chronological could be cause and effect. So one thing triggers another thing or causes another thing to happen. So "if I drop my phone" happens first right. What I mean when I say "it's not always chronological" is, that is not always the case with logic. Sometimes, things don't follow in a time-based, cause/effect type of way. For instance, let's say: if I like to watch soccer, then I like to play soccer. So me being a soccer watcher is enough for you to know I like to play soccer as well. There is no chronology here. We don't know which comes first and we don't really care. We just want to know: what is the case. If I prefer one thing, then I prefer this other thing.

So the point is, there are any number of examples like this that are not really concerned with chronology/time. I think this trips up a lot of people because we use these normally time-based words such as "if" and "then." When we use those words, we don't mean "then" as in a later point in time. Rather, we mean: if we know A, then we know B as well.