TRUTH IS NOT VALIDITY.
Truth and validity are two concepts that are as different from each other as football is from origami. Truth and validity are not the same. You should never, ever, confuse the two—especially on the LSAT.
Truth is a property of sentences (or to be more precise, declarative statements). I think we all know the definition of truth and yes, it’s what you think. For a statement like “all dogs go to heaven," it’s true if all dogs go to heaven. It’s false when it’s not the case that all dogs go to heaven. False statements are sometimes called lies.
Let’s bring the distinction home. Validity is a property of arguments. Validity is not a property of statements. Truth is a property of statements. Truth is not a property of arguments. What does this mean? Try thinking about this example. I think we all know that we can’t say about the number “2″ that it’s happy. Why? Because it just doesn’t make sense. Why? Because emotional states are not properties of numbers. Analogously, you can’t say about an argument that it’s true or false. Simply because truth isn’t a property of arguments.
I know this may come off as a little counter-intuitive at first, but that’s because you’re not used to the concepts of “validity” and “arguments” whereas you’re very familiar with emotions and numbers. But let me assure you that it’ll take no longer than… um… a month or two of hard thinking to become fluent with these concepts. Sorry, but that’s the way it is. As for validity, again, look at the definition: if (or pretend) that all the premises are true and when that’s the case, then the conclusion must also be true. See how it would make no sense to talk about whether a sentence is valid or not? Just like it makes no sense to say whether dogs are even or odd. Numbers are even or odd. Dogs are awesome.
Truth is a property of sentences. Sentences are true or false. Sentences are not valid or invalid. Validity is a property of arguments. Arguments are valid or invalid. Arguments are not true or false.