only/ only if vs. the only

[frankdio]

Maybe this question is silly but here goes,

Ok... so I get that Only if statements indicate a necessary condition.

X only if Y

X-->Y

Based on the discussion for diagraming the only statement on page 328-329... it seems to me that in this specific case the only is acting as a trigger or sufficient condition.

Or, maybe the only is modifying a different part of the sentence (students with learning disabilities)...

If only, the brilliant people at manhattan would clarify this for me

[rzaman]

I'm glad you posted since I was confused by this also. I was under the impression that "the only" was a sufficient indicator. It's pretty similar to other sufficient indicators such as "Every" and "Any" because all of these words guarantee something else. So "the only" (whatever it is) guarantees something else occurring. Like "the only students with special education needs" guarantees that they are students with learning disabilities.

Staying on topic, how do you think you translate a statement like "You are the only exception to this rule" to a conditional statement? If what I said above is correct, then wouldn't it be: (E=Exception, Y=You)

E --> Y

But I thought verbs of certainty like "are" indicate a guarantee. So wouldn't it also be:

Y --> E

So is this statement a biconditional statement? If only I hadn't just confused myself..

[giladedelman]

Good discussion!


Frankdio, you hinted at one resolution to this issue in your post. Let's look at the answer choice in question:

(D) The only students with special educational needs are students with learning disabilities.

This is not the same as saying "Only special educational needs students have learning disabilities." In fact, it's the opposite! As you suggested, "only" is modifying the second group. We can see this more clearly if we rephrase the sentence:

"Only students with learning disabilities have special educational needs."

So "only" is telling us that "learning disabilities" is necessary here.

And that's always the case: if X happens only when Y happens, then Y is necessary for X. In this answer choice, they hid the relationship a little by mixing up the sentence structure.

And as for biconditionality: that's only when we have some variation of "if AND only if."

Does that clear this one up for you guys?