Only Unless

[willyhud]

Hey PS Team,

I'm familiar with how to handle "unless". Personally I prefer to translate it as "if not" vs. the PS Bible way of making the unless condition necessary and negating the sufficient condition. ANYWAY that's just to say I'm a little confused about "only unless".

For example in this statement:

Only unless I use powerscore will I not do well on the LSAT.

I'm tempted to unpack "only unless" as equivalent to "only if not" and then the "only if" part becomes a negated necessary condition.

So the above "only unless" example would be:

[Only if not] I use powerscore will I not do well on the LSAT.

NOT do well on LSAT then did NOT use powerscore.

Is this sound?

Best,
W

[Nikki Siclunov]

Hi willyhud,

Thanks for your message. I understand your interpretation of "unless" as "if not", resulting in the contrapositive of the statement that you'd form using the Unless Equation. Either way is fine, of course, just be mindful of one caveat: the double necessary condition.

For instance:

A city cannot prosper unless its citizens are safe and its tax base solid.

Now, using the Unless Equation, it is easy to see that there are two necessary conditions for a city to prosper:

Prosper Citizens Safe and Solid Tax Base

Using your method (unless = "if not"), you have to swap "and" with "or" in order to form the valid contrapositive:

Citizens NOT Safe or NO Solid Tax Base NOT Prosper

As long as you keep that in mind, you'll be fine. But when in a hurry, it's easy to overlook it - which is why we stand by our Unless Equation

Onto your second question. "Only unless" is not a phrase I recall ever encountering on the LSAT. It sounds both ambiguous and grammatically incorrect. The only instance in which it might appear on the LSAT is when each necessary condition indicator belongs to a separate clause (one of which - subordinated). For instance:

"A driver's license is valid for one year only, unless renewed."

Which means:

NOT valid for only 1 year (i.e. valid for >1 year) Renewed

Does that make sense? Let me know.

Thanks!

[willyhud]

So helpful. Thank you so much