@bqmichael This is a really great answer!!
I'd add that before I had children, I assumed that I would spank for discipline, simply because it was what I had experienced, seemed normal, and seemed (to me at the time) effective and not problematic.
By the time my eldest was actually of an age to need discipline, I had changed my mind entirely and now I rarely even punish at all (and if I do, it's something very mild like losing a privilege temporarily). I still think that overusing punishment is
almost as bad as hitting because it has a lot of the same downsides. Hitting does tip over into being worse IMO, because most children are terrified of being hit by an adult (with good reason!) But in general trying to use aversives to make somebody behave is so different to my overall approach that it simply doesn't fit in. But I would have been totally baffled by this idea ~15 years ago!
The main thing was that I didn't know anything about parenting approaches which didn't have these aspects - I just assumed that my job, as a parent, was to teach my child and that included punishment when they did something that I wanted to discourage. It just seemed like the only logical response there. It was only really through living it (and also I did read a LOT of books, but I like reading) that I really got to a point where I just wouldn't even consider it. I now can't see any possible situation where spanking would be beneficial.
The point the above poster makes about gentle parenting being a social media buzzword is really important too. If you start out with your position being "defend gentle parenting" this is a huge umbrella and you could be looking at the parts of gentle parenting which are effective and beneficial, and/or you could be looking at the parts of gentle parenting which SOUND lovely but in practice are unrealistic or cause problems. And he in turn may look at gentle parenting and come across people critiquing some of the more ridiculous-sounding aspects (or actually ridiculous suggestions dressed up as legitimate parenting advice) or look at some of the very surface-level, tiktok/instagram type stuff and instantly dismiss it as nonsense - which, honestly, most of that is without the deeper contextual understanding (and some of it doesn't even HAVE that so it is literally nonsense).
What this can cause is that he starts to become concerned about what he perceives as a lack of structure, clarity and boundaries and consequences so doubles down on those things, fearing that he has to provide enough of them for both of you and to make up for your "coddling". And you become concerned about what you perceive as his lack of empathy and compassion and acceptance of your child and so you double down on these things, fearing that you have to provide enough of them to make up for his "coldness". And then you end up in a really unbalanced state where the stricter parent is coming down hard on the child for every little thing and the more empathetic parent is letting them off everything because "I know you didn't mean that" and this is extremely confusing and chaotic for the child. So it's important for you both to come together and see the positives in each others' approach. See if you can achieve your aims of empathy and understanding WHILE building in limits, accountability and so on - and he should see if he can achieve his aims of having clear lines and structure WHILE making some space to see his child's perspective.
So instead of "gentle parenting", I'd look at:
Attachment science, specifically four Ss: Safe, Soothed, Seen, Secure. If your home has an implicit threat of violence, then it's not a safe space. Obviously, there's a difference here between a household where a parent is randomly and frequently violent, vs a very rare occasional "big bad" punishment, but if it's been a while since either of you has been in a situation where physical discipline is used, you may have forgotten the fear that comes with it. This was actually a turning point for me; we visited my dad and younger siblings when my eldest child was a tiny baby, and during that visit one of the kids got threatened with a spanking and the atmosphere of the WHOLE house changed. Think about your child being a teenager or older primary school kid, they have done something which was silly and has got them into a mess. Do you want them to come to you and open up and ask for your help to put it right? Or do you want them to hide, lie, and cover up what they have done out of fear? Maybe you can each think of a situation that you might have had, or a friend of yours might have had, in these years and what your/his/the friend's parents' reaction to it was and what that meant for the child. The early years really build your foundation for those big situations later. I really like the Dan Siegel/Tina Payne Bryson books for info on this, especially The Power of Showing Up, but there are plenty of books about attachment (note, not
attachment parenting, but the psychological theory of attachment.) The other Ss are about providing empathy when they are upset, seeing them as a whole person not just a blank slate/in a role you have created for them (My son will be a successful lawyer and football player etc), and security is about predictability and routine, knowing they will always have a warm bed and enough food and you'll be there.
Positive parenting/modern behaviourism: If you've had dogs at all you might be familiar with a movement within animal training where rather than punishing the dog for actions that you want to discourage, you instead look for "incompatible behaviours" and reward/encourage those. For example, if you want to discourage jumping up on furniture, you would teach lie down/lie on your bed, and then prompt and reward this every time the dog tries to jump onto the furniture, which over time they internalise as furniture = off-limits. For more specific or complicated behaviour, you can use a technique called "shaping" where you identify small steps towards a preferred behaviour and reward those incrementally. Like to acclimatise a dog to a sleeping/travelling crate, you would first leave the crate fully open and reward/praise them for investigating/sniffing it, then when they go inside just for a moment, then them spending a longer time with the door open, then you briefly close the door for a moment and reward them, then you start closing the door for longer until they are perfectly happy and calm, safe in the knowledge that they will be let out. Of course, children are more complex than dogs. But essentially, the same works for humans. Discouraging what you don't want is less effective than encouraging what you do want, and when what you want is not clear, making small steps towards that is also helpful. A good resource for this is the Everyday Parenting course on Coursera by Alan Kazdin/Yale.
Early childhood development: This might just be me as a psychology nerd but I've found learning about development to be one of the most fascinating things that I could do, and one of the most useful things because it helps you figure out if your expectations are even realistic. For this unfortunately I struggle to recommend resources because I've never found one single resource which covers everything succinctly, it's all been things I have learned here and there and by observation and so on. There is a nice book called "Experimenting with Babies" which is a fun introduction (interactive, including some suggestions of things you can try out with your baby), Montessori materials are helpful for 12mo+, though you don't need toys that are marketed as "Montessori specific" and although it's not evidence based, the Wonder Weeks app can be an entertaining introduction to the idea of looking for small increments in the things that your child is perceiving, well before any discipline comes into the question. The RIE approach to baby care can also be really great in terms of getting you into a habit of observing your child and seeing what they CAN do.
Communication guides: For example, How To Talk is a series of parenting books which emphasises communication with children over reward and punishment. It can be used in conjunction with a whole load of other approaches. Really great toolkit to have. Non Violent Communication (NVC) is also a really great resource - they have parenting guides and general communication guides and there are courses you can take. This is also useful in terms of helping you and your spouse communicate in a collaborative way, without feeling like either is attacking the other.