Sufficient and necessary conditions

[lsat_novice]

I thought that all conditional statements could be turned into an if/then format and that all conditional statements consist of a sufficient condition and a necessary condition.

BUT I'm reading the introduction to The Official LSAT SuperPrep (the one with PrepTests A, B, and C) and on page 24 it says:

You don't deserve praise for something unless you did it deliberately.
You don't deserve praise for something if you didn't do it deliberately.
To deserve praise for something, you must have done it deliberately.
If you think carefully about these statements, you should see that they all mean the same thing. And you can see that none of them says that doing something deliberately is a sufficient condition for deserving praise.

Then it says...

If it rains, the sidewalks get wet.
Rain is all it takes to get the sidewalks wet
The sidewalks get wet whenever it rains.
These statements do not express necessary conditions for wet sidewalks, only sufficient conditions.

I thought the first example could be diagrammed:
Deserve praise Did deliberately

And I thought the second example could be diagrammed:
Rains Sidewalks wet

Can anyone help me sort this out please? Thank you!

[Dave Killoran]

Hi LSAT,

You are correct that every conditional statement has at least a sufficient condition and a necessary condition (I'll avoid discussing bi-conditionals or double arrows, which have two sets of each).

In the SuperPrep example, though, you've made the mistake of isolating their last sentence and they've made a mistake by not being clear (which is a good example of why conceptual discussions aren't their strength). Note what they say at the start of the paragraph: "These statements each tell us that rain is a sufficient condition for the sidewalks getting wet." That means those sentences would be diagrammed as Rain Sidewalks wet, exactly as you thought

The point they go on to make there is that you shouldn't confuse a sufficient condition as the only thing that activates the necessary; others things could as well (such as someone using a hose, or an open fire hydrant). The last sentence is accurate because they are talking about the idea in relation to wet sidewalks, but it's badly presented in the context because they make it seem like a universal statement (it wasn't meant to be, and isn't true universally). It's not mean to be, and technically when you have a conditional statement, once you get one part of it, the other gets defined along the way (such as in every single one of their example sentences).

Please let me know if that helps. Thanks!

[lsat_novice]

Thank you!

[miriamson07]

Even though a conditional statement always has a necessary and sufficient condition, the opposite isn't true, right? As in, a necessary/sufficient condition doesn't have to be part of a conditional?

[Dave Killoran]

They actually have exist together at some point in a conditional relationship. Meaning, something isn't a sufficient condition unless somewhere there is a necessary condition for it (and the reverse is true, too). But, once you have a conditional relationship somewhere, you can have isolated pieces in other sentences in an argument, which is what I think you are driving at here.

So, for example, we can have an argument like the following: "It's been raining all day. And of course when it rains, the sidewalks get wet. So the sidewalks are wet." When reading that first sentence, we have a sufficient condition, although at the time we don't know it yet. We don't discover that to be the case until the second sentence where the full conditional relationship is presented. Then the last sentence--which is the conclusion--states that the necessary has happened. So you have a sufficient condition, then the full conditional relationship, then just the necessary at the end. So individual conditions can exist outside the conditional sentence.

But ultimately, if someone talks about a sufficient or necessary condition individually, somewhere there has to be a relationship between the two (otherwise how would you know one is sufficient or necessary?).

Thanks!