(Long response to MrWiggles, two three posts ago, now.)How about Understandings having a magnitude (or an analogue of magnitude from "Farming" being superseded by "Farming2", except... well... better). ((Or, indeed both. "Harvesting" perhaps being level 1, "subsistence farming" for level 2, "social farming" (needs a better name) further up, then onwards until "industrial farming" (which in this example I'm claiming as an "understanding" name) and perhaps beyond, but, again, each level having its own magnitude on top of the basic presence of the Understanding.))
The tech
Applications require certain degrees of a certain number of Understandings. "Mechanised Farming" as an Application requires either the Industrial Farming Understanding or perhaps
several of the higher-level farming Understandings to various degrees (plus whatever non-farming Understandings allow tractors, etc) and gets a bonus to effectiveness for the sum of the
excess degrees that you have above the basic number necessary in the spec[1]. (I could envisage the spread of these excesses dictating the nature of the bonus[2]. An excess in the Farming area would perhaps give an increase in yield, while an excess in the tractor-esque Understanding(s) would give an increase in speed of harvesting. Surprising bonuses could be implemented by setting a certain farming-type Application to 'require' chemical engineering at level
zero, but for each excess level you get a fertiliser/pest-control bonus to production. It need not be publicised as "needs zero levels", even, but with higher levels of Farming Applications having a non-zero requirement it would effectively mean an early adoption of that aspect of ancillary farm-tech is rewarded without actually being
required, just yet.)
Without the 'tractor-factor', whatever that might be in terms of Understandings, your Industrial Farming Understanding would still be useful, albeit in a form of farming that still involves manual labour (with an
army of farm-hands producing high yields on the land), because there'd be an Application tuned to
that, as well. Perhaps requiring something like Socialist Ideals or Enforced Feudalism behind it, of course, to the appropriate degree (and probably some suitably attuned social settings for your little empire).
As with the Great Library wonder of Civ fame (but automatically, although doubtless augmented by some cultural exchange institute or other, as well as spy networks and intellectual treaties with friends), higher level Understandings (or higher levels
of an understanding) could leak into your civilisation (and leak out by similar means, of course, whether you like it or not, although you'd have a limited capability to stem the flow according to various policies). It would thus be inevitable that any nation-group (or however you organise players/NPCs, e.g. homeworlds) that were not totally isolationist could gain some higher level of farming (though not up to the level of those who were advancing that tech) even if they'd been mostly concentrating on some other field (NPI!) of technological improvement unless they'd stagnated long enough in that field for you to catch up and be their equal, by which time
every farm-idle civ would probably have the same base Understanding cohort.
And then, at the other 'end' of the tech-level spectrum, how about Applications also having an
upper limit to some Understanding levels? Your manually-powered Industrial Farming-led Application which benefits from your Socialism/Feudalism/whatever is cut-off from use as some other social-upheaval Understanding, as the people no longer want to be slaves to agriculture. This could be done by degrees... As the City Living Understanding (if that's one of the 'poison in the chalice' items) is developed in order to sustain a burgeoning industrial revolution in other areas of the tech-tree, each level increases the
cost of maintaining the army of labourers that you need, thus making this form of farming impractical and requiring you to quicken development of less labour-intensive means.
(Or... to extend the example further either an Understanding or a social factor that allows Immigrant Workers to happen can factor in (amongst many other things it does) an offset to this penalty... but by now I can see that I'm already over-writing just this one
branch of possibly tech applications, so Gods know how much effort you'd want to put in to tune a complete structural system with all these additions and caveats!)
So, anyway... feel free to pluck out any bits you like. If any!
[1] If you want it to be more complicated
(fakeedit: hah! ...I wrote this before I did go more complicated with the last few paragraphs!) the spec could include "foo>1, bar>2, foo+bar>4", so "foo=2, bar=2" is valid, as is "foo=1, bar=3", but not "foo=1, bar=2" or even "foo=3, bar=1"... (This might also mean you can set a variable-makeup Application to be "FooA>0, FooB>0, BarA>0, BarB>0, BarC>0, FooA+FooB>1, BarA+BarB+BarC>2", allowing
either FooA or FooB to be the 'Fooish' requirement, and any
two of BarA, BarB and BarC. Assuming you'd also accept two levels of any
single Bar, also[1a].
)
[1a] "min(BarA,1)+min(BarB,1)+min(BarC,1)>2"? In the game internals, that'd work with an appropriate parse-friendly structure to associate with each research object, but starting to get messy from the player's POV if you're trying to convey this information to them at all without a freetext description of the requirements tagged into the research management system.
[2]
Additional fakeedit: with reference to the above footnote, I'd make the "excess levels bonus" countable from the individual minimums, so [2+2] means an automatic foo-bonus, while [1+3] makes an automatic bar-bonus. This would straight away 'flavour' the nature of the Application to whichever of the requirements you "made up to excess" in order to arrive at the sum total part of the spec. Whether you'd grant these bonuses special status (attain a pest-control bonus on gaining such a dependent farming Application and you get a permanent buff factor on top for all
future stages, but attain the speed bonus and
that is made into a permanent buff... mutually exclusive, of course, unless the engine allows simultaneous advancements[3]) or just allow the hypothetical next development towards [2+3] (one level of buff for each, now) absorb the benefit, I don't know... It's not my system, so do as you think best.
[3] I don't think it should. Even if you strive to simultaneously obtaining a further level of foo the one from a university exchange program with the Fooier civilisation while your spies bring back the next level of bar from the Barier one, I say that it should be a pot luck choice as to which happened, or else you'd also have to consider
closely-timed occurrences. See, even
more complicated!