Many dog breeds are herders, retrievers, hunters, it's instinctual to chase moving animals, like cats. These dogs don't want to kill them, just herd retrieve or hunt. Most of the remaining dog breeds either want to play, ignore, or make friends with family cats. Generally speaking, dogs and cats in the same home or neighborhood get along fine, although there's always exceptions to every rule.
That's almost a myth. There are many people that own both as pets and they don't fight. Dogs are natural hunters (as are cats), yet dogs are larger and not as lazy. Cats make easy targets since they are usually lazy.
if you put two cats together, they fight and hiss but if you train them together and let them get used to the other, they will like each other. it's the same way for a cat and a dog, train them together and they won't fight. it's all about the smell, they don't like that the other is different.
some do some dont. my grandmas dog and cat get along great and the actually sleep in the same.bed as each other. that cat sleeps with the dog on the dog bed. now others fight and attack each other each animal is different