Research goals

When I'm researching, say , I pick one of six research goals. When that goal is achieved, oftentimes the game presents me now with a choice of only three research goals.

What is the rule for this? Why am I not unrestricted in backfilling?

This thread contains a detailed explanation of how to determine which techs will be available to research. In short, it's a mechanism that was carried over from Civ2. The thread contains an Excel spreadsheet that lets you make the necessary calculations. I don't know if this spreadsheet works in modern versions of Excel, since I no longer have that program.

That should answer your question about what is the rule for determining available tech choices. In practice, I doubt that current players use this information. You just learn that certain key techs may not be immediately available to you. As to why the game works this way, I think the developers simply wanted to introduce some randomness into tech availability so that players wouldn't be able to count on beelining to important techs.

Well, isn't that beyond confusing. n + t mod 3 != 0? Who writes this stuff?

Anyway I don't have Office so I can't view the excel file. It's enough for me to know there are arcane rituals and ablations I must perform to appease the tech selector.

... Thanks.

I recommend blind research (or double blind), making the game's course a bit lesser to predict