Introduction:
This question is regarding whether the word "dog" is a proper noun or a common noun.

Explanation:
Definition of Proper Noun:
A proper noun is a specific name given to a person, place, or thing.

Definition of Common Noun:
A common noun is a general name given to a group or category of people, places, or things.

Analysis of "Dog":
Dog can be analyzed in two different ways:

1. As a general name for the animal species
2. As a specific name for an individual dog

General Name for the Animal Species:
When "dog" is used as a general name for the animal species, it is a common noun. For example, "The dog is a loyal and friendly pet."

Specific Name for an Individual Dog:
When "dog" is used as a specific name for an individual dog, it is a proper noun. For example, "I named my dog Max."

Conclusion:
In conclusion, whether "dog" is a proper or common noun depends on the context in which it is used. If it is used as a general name for the animal species, it is a common noun. If it is used as a specific name for an individual dog, it is a proper noun.