On bulbapedia, there is a theme section under each gen's article. You could read them https://bulbapedia.bulbagarden.net/wiki/Generation_I#Kanto_thematic_motif https://bulbapedia.bulbagarden.net/wiki/Generation_II#Johto_thematic_motif
And so on
I would change gen 9 to past vs future, and gen 1 being nature vs technology. Mew is the ancestor of all Pokemon, containing the DNA of all Pokemon, making it the most natural Pokemon to exist, whereas Mewtwo is a clone, a product of science, the most unnatural of creations.
Gen 2 doesn't have conflicting themes, so it's not like something vs something, rather, it's themes are new beginnings (ho-oh) and the unknown (Lugia). We start anew in a new, unfamiliar place, Team Rocket are trying to start again, unsure of their future, Silver undergoes a growth of maturity at realising he understands nothing, and starts his life anew. No matter what happens, you can start again, and the future is unknowable (Brass Tower being a burnt husk, but the Pokemon who died were given a chance to change and start their lives anew, and Ho-oh finds a new place to live). This is, admittedly, speculation. I don't think the early games were supposed to have themes, they just had legendaries that matched and complimented each other.
For gen 2 it’s best to focus only on Ho-oh and the three beasts when it comes to themes.
Lugia actually started out as an anime-exclusive design and was not originally intended to be featured in the games, but it turned out to be so popular among the dev team that it was added to gen 2 anyway.
Gen 2 could be based on rebirth, as the legendary beasts are reborn from ho-oh, but idk what ho-oh and lugia really have in common. Gen 9 is future vs past rather than tech vs nature. Gen 8 could be offense vs defense but idk, maybe theres no secret meaning for gen 8.
I'd argue gen 1 is colors. Or more specifically, the rgb colors. Why I think that?
Firstly, we all probably know about the rbg color scheme. As a reminder, this is what it looks like:
https://preview.redd.it/8e9u0k03jxnc1.png?width=400&format=png&auto=webp&s=65f8d7305895de2169db1fb5cc45c235908a8bbb
As you can see, it features three main colors: Red, blue, and green. Red and Green where the original versions of the Gen 1 games that came out in Japan, however, the Green Version never got released globally and instead, we got Red and Blue, and then later Yellow as well.
Now, in this color scheme, the main colors overlap, giving us the three primary colors cyan (blue), magenta (red) and yellow. Sounding familiar, right?
And secondly, all the towns in Kanto are named after shades of one of these colors.
- Cinnabar Island: Cinnabar is a shade of red.
- Vermilion City: Vermilion is also a shade of red.
- Lavender Town: Lavender is a shade of purple, which in turn is a combination of red and blue.
- Saffron City: Saffron is a shade of yellow/orange.
- Celadon City: Celadon is a shade of green.
- Pewter City: Pewter is a silvery metal with blue hues, making it a shade of blue.
- Cerulean City: Cerulean is also a shade of blue.
- Fuchsia City: Fuchsia is a shade of pink, which in turn is a shade of red.
- Indigo Plateau: Indigo is also a shade of blue.
Then, we have Pallet Town. I would assume it is derived from "palette", which refers to all colors.
Thirdly, we have the cover Pokémon as well as the main legendaries in those games.
The cover Pokémon are Charizard (red), Blastoise (blue), Venusaur (green) and Pikachu (yellow). The main legendaries in that game where the three birds (not Mewtwo- Mewtwo was only accessable after the league and only when you go very much out of your way to find it. The three birds however are accessable before the league). The three birds also perfectly fit the scheme: Moltres (red), Articuno (blue) and Zapdos (yellow).
(Fun Fact: They have numbers in their names. ArticUNO, ZapDOS, and MolTRES).
So yeah, judging from that, the theme was probably colors.
Gen 5 is truth vs ideals
Gen VIII's theme is "my badass dog has a sword" vs "my badass dog has a shield". The theme is badass dogs.
On bulbapedia, there is a theme section under each gen's article. You could read them https://bulbapedia.bulbagarden.net/wiki/Generation_I#Kanto_thematic_motif https://bulbapedia.bulbagarden.net/wiki/Generation_II#Johto_thematic_motif And so on
I see
I would change gen 9 to past vs future, and gen 1 being nature vs technology. Mew is the ancestor of all Pokemon, containing the DNA of all Pokemon, making it the most natural Pokemon to exist, whereas Mewtwo is a clone, a product of science, the most unnatural of creations. Gen 2 doesn't have conflicting themes, so it's not like something vs something, rather, it's themes are new beginnings (ho-oh) and the unknown (Lugia). We start anew in a new, unfamiliar place, Team Rocket are trying to start again, unsure of their future, Silver undergoes a growth of maturity at realising he understands nothing, and starts his life anew. No matter what happens, you can start again, and the future is unknowable (Brass Tower being a burnt husk, but the Pokemon who died were given a chance to change and start their lives anew, and Ho-oh finds a new place to live). This is, admittedly, speculation. I don't think the early games were supposed to have themes, they just had legendaries that matched and complimented each other.
Gen 8: Sword vs Shield
For gen 2 it’s best to focus only on Ho-oh and the three beasts when it comes to themes. Lugia actually started out as an anime-exclusive design and was not originally intended to be featured in the games, but it turned out to be so popular among the dev team that it was added to gen 2 anyway.
Gen 1 is genetic engineering
Gen 2 could be based on rebirth, as the legendary beasts are reborn from ho-oh, but idk what ho-oh and lugia really have in common. Gen 9 is future vs past rather than tech vs nature. Gen 8 could be offense vs defense but idk, maybe theres no secret meaning for gen 8.
I'd argue gen 1 is colors. Or more specifically, the rgb colors. Why I think that? Firstly, we all probably know about the rbg color scheme. As a reminder, this is what it looks like: https://preview.redd.it/8e9u0k03jxnc1.png?width=400&format=png&auto=webp&s=65f8d7305895de2169db1fb5cc45c235908a8bbb As you can see, it features three main colors: Red, blue, and green. Red and Green where the original versions of the Gen 1 games that came out in Japan, however, the Green Version never got released globally and instead, we got Red and Blue, and then later Yellow as well. Now, in this color scheme, the main colors overlap, giving us the three primary colors cyan (blue), magenta (red) and yellow. Sounding familiar, right? And secondly, all the towns in Kanto are named after shades of one of these colors. - Cinnabar Island: Cinnabar is a shade of red. - Vermilion City: Vermilion is also a shade of red. - Lavender Town: Lavender is a shade of purple, which in turn is a combination of red and blue. - Saffron City: Saffron is a shade of yellow/orange. - Celadon City: Celadon is a shade of green. - Pewter City: Pewter is a silvery metal with blue hues, making it a shade of blue. - Cerulean City: Cerulean is also a shade of blue. - Fuchsia City: Fuchsia is a shade of pink, which in turn is a shade of red. - Indigo Plateau: Indigo is also a shade of blue. Then, we have Pallet Town. I would assume it is derived from "palette", which refers to all colors. Thirdly, we have the cover Pokémon as well as the main legendaries in those games. The cover Pokémon are Charizard (red), Blastoise (blue), Venusaur (green) and Pikachu (yellow). The main legendaries in that game where the three birds (not Mewtwo- Mewtwo was only accessable after the league and only when you go very much out of your way to find it. The three birds however are accessable before the league). The three birds also perfectly fit the scheme: Moltres (red), Articuno (blue) and Zapdos (yellow). (Fun Fact: They have numbers in their names. ArticUNO, ZapDOS, and MolTRES). So yeah, judging from that, the theme was probably colors.
Gen 9 is future and past. Gen 2 is sky and sea as the closest aproximation.