As long as they don't meet, I don't see why not. Depending on the dimensions you might be able to come up with a layout pattern that uses both tiles and have the same on both walls. Why do you want to use different tiles? Are they on clearance or something?

I'm using 16x16 tile on my countertops with matching 12x12 tile along the back cut to 8" width. Fronted with a contrasting 3x12 bullnose. Wood trim to hide the edges of the plywood/hardibacker mounted flush below the bullnose.

Then the 4x12 pieces left over will be the bottom row of my backsplash, then above that about 2.75" width of glass mosaic, then a full 12x12 row of tiles, topped by a 4.25" width of the same mosaic. I'm mixing 4 different tile sizes, LOL! More if you count the fact that the mosaic tile is of varying lengths, 2", 8", and 4" long pieces. We won't count the tiles that have to be cut to fit.

The cabinets on the right end of the L-shaped counter are lower so there won't be room for the upper layer of mosaic and the 12x12 row will have to be cut short, about 10.25".. Only 2 rows of mosaic will fit under the range hood mounted to the left of the sink, then a full 7 rows of mosaic where it comes out the other side of the hood. I'll trim along the far left edge with wood trim thick enough to hide the raw edges of the tile and the underlying hardibacker.

How many colors - lets see, the mosaic has 3 colors of glass and one of porcelain. The 12x12 and 16x16 tiles match. The bullnose is in contrast. So 6 different colors. Who wants a samey-samey backsplash?

You can do whatever you want. May I ask why you want to do this?

absolutely out of the question. Someone will think of this as a mistake and wonder what other "mistakes" did you make? I wear mismatched plaids, and colors that don't always go well together....but things affixed to your house-NO WAY...You better NOT.

Do what you want. Any idiot who thinks using different tiles in different spots is some kind of "mistake" that means the house will fall down isn't worth worrying about.

What size are these tiles? Can you post a few pics and the dimensions and why you are thinking of doing it this way?

Plenty of photos of different tiles used on different sides of a kitchen can be found on Houzz, you just have to set aside the time to do it. I probably spent an hour each night for the last 2 weeks saving photos to my ideabooks to narrow down the look I want for my back splash.

You absolutely can. Do you have a pic of the two walls? I'm wondering if there's a way to actually pull some of the small tiles onto the subway tile side and some of the subway tile onto the small tile side. Then it would definitely look like it was done intentionally as a design move.

"It doesn't seem very zen-like to call other forum members idiots."

I repeat - any one who thinks using different types of tile in different places is a mistake that means the house will fall down is an idiot. It isn't zen, it isn't not-zen, its just a fact.

Even more idiotic is working yourself up into a lather over whether or not some generic future home buyer is going to like your choices or not. And that is NOT what I am saying or even trying to imply the OP did - but an awful lot of people DO do this, and let themselves be browbeaten in to things they don't want and/or don't even LIKE because they let other people scare them with the no-one-will-ever-buy-your-house heebie-jeebies.

My house is going up for sale as soon as possible. I'll still be painting the accent wall in the LR turquoise, and an accent wall in one of the bedrooms in watermelon. If the next person doesn't like it, they can repaint. It's not rocket science. Ditto whether or not they like my backsplash and the way I strip and repaint the original 60 year old built in cabinets. They can rip it all out and replace it if they hate it that much. Trying to guess other people's taste is a waste of time and energy. You don't even know who might be coming around when sale time comes! (I don't even know for sure when the house will go up for sale, but it can't be too soon and it's already been too long, LOL!)

Do what you want with your own house. That IS zen.