For nine months, Izzie only ever encountered Good Dad. He’s a nice guy, a caring guy. He hugs her when she’s sad, feeds her when she’s hungry, kisses her when she smiles. He sings her songs at bedtime, acts like a loon to make her laugh, and gives her everything she wants. He’s a big, cuddly bundle of fun.

The past few weeks, there’s been a new guy on the scene: Bad Dad. And Izzie doesn’t like him nearly as much.

‘Ba-da,’ she cries. ‘Ba-da!’

She’s reached the age where she’s increasingly mobile, increasingly opinionated, and increasingly capable. She watches everything you do, and you can almost hear the cogs whirring inside her skull as she works things out. Like the velociraptors from Jurassic Park, it’s a problem-solving intelligence that is scary when combined with her baby-Superman-lifting-a-car strength.

Mostly, it’s small stuff. She can take off her nappy, help herself to her biscuits by swiping them out the pocket of the changing bag, and yesterday proved she can stand without any support (though when she realised we were watching her she grabbed onto the sofa). And if she gets her hands on the baby wipes, she opens the packet and pulls them out one by one, creating a big wet mess in the middle of the carpet.

Far more alarming are her attempts at overcoming safety features. She’s figured out where she has to grab to open the stair gate keeping her out of the kitchen, but luckily doesn’t have the strength or dexterity to do it yet. When you strap her into the car seat or high chair, her fingers move to the buckle the second you move yours away as she struggles to press the release button. And when you change her nappy, she knows the exact moment you’ll be looking to the left (to pick up the clean nappy) and uses that split second to roll to the right, crawl past your thigh and make a break for the door – which she’s figured out how to open.

Into this repertoire of experimental behaviours she’s recently introduced a number that could be categorised as ‘How to manipulate mummy and daddy’. They are, from mildest to I-want-to-die-est:

1. The throw-your-bottle-on-the-floor-for-attention.
2. The pouty bottom lip.
3. The fake cry.
4. The angry shout.
5. The lose-all-control-and-scream-like-a-wild-animal-that’s-being-poked-with-a-red-hot-poker-until-you-start-to-choke-and-then-turn-purple-in-order-to-get-your-own-way.

This last one is used every time she’s put in the play pen, every nappy change, every costume change, every time I take her out of the bath, and every time I take something off her.

And so, in response, I have had to break out Bad Dad.

Bad Dad is tough but fair. Bad Dad tells her no when she’s pulling hair, or trying to open the door to the hall, or going into mummy’s handbag. Bad Dad takes car keys off her, and TV controllers, and the dog’s toys. And Bad Dad doesn’t take any shit.

No matter how much Izzie cries, screams and pitches a fit, Bad Dad doesn’t let her get her own way. She completely understands the word ‘No,’ but it’s a battleground right now as she tests the boundaries to see what she can get away with.

‘Daddy says No? I’ll reach for it again. Oh, he still says No. In that case, I’ll stick out my bottom lip and – wow, it’s still No. Maybe if I cry a bit, real tears even, now I’ll just reach out – nope, that didn’t work. I’ll shout as I reach for it – damn it, I’ll just throw a full-blown tantrum, then he’ll have to give it to me.’

To be honest, I don’t like Bad Dad either. He’s nowhere near as fun or as happy as Good Dad. He’s mean and unkind and strict and severe. He hardens his heart to his daughter’s tears and holds her while she sobs, even though he was the cause of it all, and it would be so easy to make her happy by giving her what she wants.

But Bad Dad doesn’t give in, no matter how hard it gets, and how much it upsets him, because he’s as good a dad as Good Dad. And it takes both personas to be the father of a happy, well-adjusted daughter.

But I know which one I prefer.