Novice bird-watcher: I don’t know much about animal tracks, but I do know that Support birds typically have four toes, and Support most birds have three toes pointing forward and one toe pointing backward. █████ ████ █████ ███ ████ ██ ██ ██████ ████ ████ █████ ██ █████ █████ █████ ███████ ███ ███ ██████ █████████ ██ ███ ████████ ██ ███ ████ ██ ████ ████ ██ █████
The bird-watcher knows that birds typically have four toes and that most birds have three toes pointing forward and one pointing backward. He sees a track from an animal with exactly that toe pattern, and from that he concludes the track came from a bird.
The premises establish if it's a bird, then it tends to have 3-forward-1-back toes. The conclusion needs the reverse direction: if it has 3-forward-1-back toes, then it must be a bird.
Imagine a four-toed reptile (i.e. not a bird) with the same toe layout walking through the same patch of dirt. Nothing in the stimulus rules that out. For the bird-watcher's inference to work, he needs an extra premise that the stimulus never gives him: only birds have this toe pattern.
The argument is flawed because ██
relies on the █████████ ██ ███ ████ ███████████
"Track" isn't being used in an ambiguous way. Both the bird-watcher and the reader take it to mean the footprint left in the ground, and that meaning never shifts during the argument.
does not define █████ ██ ███████ ████ ████ ████
Not defining birds as four-toed animals isn't why the argument is unpersuasive. In fact, defining them that way wouldn't help: the stimulus itself only says birds typically have four toes, not that all of them do. And even with such a definition in hand, the argument still wouldn't rule out non-bird animals that also happen to have four toes.
fails to identify ████ ████ ██ ████ █████ ████ ████ ███ █████
The conclusion is just "some kind of bird," not a specific species. The argument never needs to nail down whether it was a robin or a sparrow. Even if the bird-watcher pointed at a specific bird, that wouldn't address whether a non-bird could have made the same track.
does not establish ████ ████ █ ████ █████ ████ ████ ███ █████
The premises support "birds have 3-forward-1-back toes." To get to "this track was made by a bird," the argument needs the reverse: that only birds have 3-forward-1-back toes. Without that, any other four-toed animal with the same toe layout could have left the track, and the conclusion doesn't follow.
depends on evidence █████ ██ ██████████ ████ ██████ ████ █████ █████ ██ ███████
The argument runs entirely on evidence about birds in general ("birds typically have four toes," "most birds have three toes pointing forward..."). No individual bird is cited as a data point.
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