The sentence should be strong or weak,explain with a diagram.Please help

Question

I think the sentence is weak

All dogs can bark. No bird that can fly can swim. So no dog can bark.

Answer 1

http://www.m-w.com/dictionary/fallacy

http://www.nizkor.org/features/fallacies/
"A fallacy is, very generally, an error in reasoning."
Scroll down and read the examples on the left.

http://www.unc.edu/depts/wcweb/handouts/fallacies.html
Scroll down to What are fallacies?