If there are sentient beings on planets outside our solar system, we will not be able to determine this anytime in the near future unless some of these beings are at least as intelligent as humans.
Conclusion
If there are sentient beings on planets outside our solar system, we won't be able to determine this anytime soon unless some of them are at least as intelligent as humans.
Evidence (X and Y)
We won't be able to send spacecrafts outside our solar system anytime soon. and Any sentient being on another planet capable of communicating with us in the near future would have to be as intelligent as we are.
Evaluate
There's a lot of symbol matching and conditional logic here, so we might go down the road of diagramming (watch the class recording, via the ▶︎ button on the highlighter toolbar, if you'd like to see a diagramming discussion).
But essentially the argument boils down to this missing link: if we can't send spacecraft there, then we'll need these aliens to be capable of communicating with us.
If we translate the "unless" in the conclusion into "if-not" form, the conclusion is saying, .
Why?
Because, .
We're trying to line up the Conclusion's verbiage with that of the Evidence so that it's clearer what's being assumed.
If I say, , then I'm assuming .
This argument is saying,
So it's assuming, .
We might skeptically attack that assumption by thinking,
The author would say,
We would then reply, "the only way for us to determine their existence is to send spacecraft there or have them communicate with us? Why are those the only two ways? Couldn't we detect their presence through some sort of bio-marker we can observe via spectral analysis? If they're communicating with each other via radio waves, couldn't we potentially pick up on their signal with a radio telescope? They might not be smart enough to send a signal to us, but we might be smart enough to detect signals they're sending to each other."
Goal
The author needs to rule out alternative modes of discovering sentient beings. In his head there are only two ways: 1. send a spacecraft 2. the aliens are capable of communicating with us
The author has established we can't do #1 anytime soon and thus is thinking that #2 is the only hope, but maybe there are other ways he's failing to consider.
To lock in his conclusion, we need an answer to convince us that these are the only two ways.