Final answer:
To fix the sentence, insert a conjunction with comma or split into two sentences for clarity. The logical argument about desserts being low fat is invalid, as the counterexample of buttercream cake shows not all desserts are low fat.
Step-by-step explanation:
The sentence 'I think cupcakes are the best dessert my best friend thinks ice cream is the best dessert' should be corrected to ensure clarity and proper punctuation.
One way to fix the sentence is by adding a conjunction and comma: 'I think cupcakes are the best dessert, but my best friend thinks ice cream is the best dessert.' You could also split it into two sentences: 'I think cupcakes are the best dessert. My best friend thinks ice cream is the best dessert.'
In terms of the logical argument provided, the assertion that all desserts are low fat because all desserts are sweet and some sweet foods are low fat is invalid.
The introduction of the counterexample of buttercream cake is an excellent way to show this. Buttercream cake is indeed a dessert and sweet, yet it is known for being high in fat. This example clearly disproves the original argument by showing that not all desserts are low fat.