For example

let inline speak (a: ^a) =
    let x = (^a : (member Speak: unit -> string) (a))
    printfn "It said: %s" x

    let y = (^a : (member MakeNoise: unit -> string) (a))
    printfn "Then it went: %s" y

type Duck() =
    member x.Speak() = "I'm a duck"
    member x.MakeNoise() = "quack"

type Dog() =
    member x.Speak() = "I'm a dog"
    member x.MakeNoise() = "grrrr"

let x = new Duck()
let y = new Dog()
speak x
speak y

Outputs:

It said: I'm a duck
Then it went: quack
It said: I'm a dog
Then it went: grrrr