Unable to research despite having prerequisites

[Renergy]

Sometimes, it is impossible to choose certain technology despite having all the prerequisites for it. Typical examples are Republic and Railroads. You have Code of Laws and Literacy (or Bridge Building and Steam engine), yet The Republic/Railroads does not appear on the list of techs you are offered, so you have to select some other (random) technology (usually one) before the desired one. I have not found any definite pattern, as far as I can tell sometimes this happens, sometimes not. This delays beelining (a bit).

Wonder if this has been discussed before?

Edit: added a savegame. Already have Ceremonial Burial, Alphabet, Writing, Code of laws, about to research Literacy. After it comes up, "The Republic" should be theoretically researchable, yet it is not.

 

[darkpanda]

I remember having noticed that when on levels higher than Chieftain... I suppose higher difficulties add a random factor for you to select available techs, maybe?

 

[Mize]

I managed to dig up this old thread:
http://forums.civfanatics.com/showthread.php?t=323140

I think it explains everything you need to know, even though it might be a little confusing. Essentially, the game has an algorithm, which prevents you from researching some technologies, depending on the advances you've already made. It's not a bug. It is supposed to introduce some randomness to science research, but it is controllable if you're up to the task of doing the math every time you select a tech.

 

[Renergy]

I managed to dig up this old thread:
http://forums.civfanatics.com/showthread.php?t=323140

Thanks a bunch, Mize, that thread explains the problem to bits, especially the following post:
http://forums.civfanatics.com/showpost.php?p=8146997&postcount=11

Look at the science advisor's display when researching future tech.
The advances are listed in the same order as Urtica dioica's list. Initially, when you have no advances, the denied advances are in column 2. With one discovery, the denied advances are in column 3. Next, denied advances are in column 1. The cycle repeats.

Urtica dioica is the real "father" of the idea
http://forums.civfanatics.com/showpost.php?p=8140650&postcount=5

Dack's comment is also worth reading
http://forums.civfanatics.com/showpost.php?p=9423840&postcount=18


Thanks again for clearing this up!

 

[Osvaldo Manso]

I remember reading that this was a specific feature introduced in the game by Sid Meier in the final stages of production. As far as I remember, Sid felt that players should not have every tech available and an element of randomness should be introduced.