Can't trade tech

[Manfred Belheim]

What is it that decided whether an AI can trade a tech with you? For instance, in my current game, everyone seems to have combustion, but none can trade it with me, even though I have the tech right before it on the tree, Railroad, and can research it myself.

 

[Sisiutil]

Hover your mouse over the red-lined text in the leaderhead screen to find out why they won't trade it to you:

1. "We fear you are becoming too advanced" (a.k.a. WFYABTA) = We've seen you make X number of tech trades with us and other civs and that exceeds our programmed limit (which varies for each leader). IIRC, there's a random chance of a random number of previous tech trades being "forgotten" each turn, in which case the leader will be willing to trade techs until the limit is reached again. Being at "Friendly" overrides WFYABTA.
2. "We have our reasons" = This tech enables a wonder and we're building it. Talk to us when the wonder race is over.
3. "We just don't like you enough" = Your diplomatic score with us is too low for us to consider trading this tech to you. Some flowers and chocolates might be in order, but don't hold your breath.
4. "No thanks, we'd rather win the game" = This tech directly enables a space ship part. I may just be an AI sprite living in your computer, but I wasn't born yesterday.
5. "We don't want to go trading away this technology just yet" = We may have a monopoly on this tech, in which case we won't trade it to you unless we're at Friendly. If we don't have a monopoly on the tech, its programmed value to us is higher than other factors needed to override that, such as the number of other AIs we know of who possess the tech, your diplomatic score with us, and so on. Talk to one of CFCs many XML experts for more detail on this one.

 

[Manfred Belheim]

Oh I see... so "Can't trade" in the tech advisor screen just means "won't trade" then. I thought they literally couldn't.

 

[Sisiutil]

That's different. "Can't trade" literally means just that.

Usually you'll run into the situation you describe if you acquired a prerequisite technology on that very turn through a trade. (It doesn't happen for a tech you just finished researching because, technically, you finished researching it at the end of your previous turn.) For example, if you acquired Railroad through a tech trade, then Combustion will be listed under "Can't trade" on that turn. Proceed to the next turn and that will change.