32 LR One Question 24
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How can brown dwarves have lithium if they are defined as having less mass than stars, but only objects that have more mass than the sun have lithium? How can we make any statement about whether all brown dwarves have lithium or not?
Ah, but the passage didn't say that only objects with more mass than the sun have lithium. It said that all stars with more mass have lithium.
Brown dwarfs must not be stars, since we're told that they do have lithium, and that they are smaller than stars.
If all brown dwarfs have lithium then why does the passage state they are partially defined by whether or not they have lithium. If they all have lithium, then that factor would not contribute at all to their definition.
In order to define any group by a trait, it's necessary for all members of the group to share that trait.
We define "mammals," for instance, in part by the fact of their warm-bloodedness. All mammals are warm-blooded, so if some creature is cold-blooded, we can be sure it's not a mammal.