A bottle of Shampoo
A bottle of Soap.
Both are of the same category; toiletries. Both more or less contain the same things.
you can use different brands of shampoo but the purpose remains the same, and this logic applies for soap also.
But do you use a soap like a shampoo?
And do you use a shampoo like a soap??
Without purpose, there wouldn’t even be humans in the first place, or equivalent.