What are the basic ideas making up Celtic mythologies?

Well, there's many gods - you'll find the main majority of them referred to as the Tuatha de Danaan (TdD), but that doesn't cover all of them. There's some "major" ones, but different areas and different tribes did worship different gods (or placed different significance on different gods).

Evil showed in several ways - the Fomor, for instance, were... semi-evil, but only in the sense that they represented the forces of chaos and destruction.

There's no known story about the beginning of the world for the Celts. There's something called the Prophecy of the Morrigan, which some consider a prophecy of the end of the world, but that's up for debate.

It wove itself into daily events, really. Druids made calendars recording which days were lucky and unlucky, based on certain omens and portents. Folks consulted with Druids on major events. Stories were told about interacting with the Otherworld. Religious holidays were celebrated as a community.... Honestly, it played into Celtic life the same way that Christian beliefs played into Christians' lives for most of two millenia.

The fact is you are asking the unknowable. Caesar tells us the druids forbade writing down of most of their lore because they said it enabled people to forget it. Most of what we know about it comes from after the Druids' Power was broken and often after Christianization -- the Book of Invasions is known from three manuscripts one by Michael Cleary which really means Michael the Cleric. On top of that the Celts seemed to worship local gods and goddesses who by their nature could be the same as or different from others who presided over the same things. They were a broad and widespread people.

There are no stories about the beginning or the end of the world outside the Medieval context -- in other words Celtic versions of Bible Stories. Some evidence suggests they believed in reincarnation. But evil is manifested in foul deeds in the legends we have.

This woman has amassed all the knowledge we have about Celtic beliefs and publishes it on her website:

http://www.maryjones.us/

such loads of celtic thoughts. I do consider the guy above me about the secret of Roan Inish. large movie. there is a few thoughts about Fionn MacCumhail (reported Finn McCool, each and every so often spelled that way besides). there is the tale about him and why he sucks him thumb previously he is going into conflict. the mandatory theory: some large sensible human being (won't be able to bear in mind who this replaced into for the existence of me) exhibits the fish of understanding and tells Fionn to practice dinner the fish over a fireplace so he (the sensible human being) can eat the fish to achieve a lot of understanding. even as Fionn replaced into cooking the fish it began to bubble and blister. He pressed the fish down with his thumb to provide up the effervescent. for sure it replaced into warm and in the present day positioned his thumb into his mouth. He gained the understanding from the fish. So, that replaced into why he continually sucked his thumb previously he went into conflict. His spouse Sadbh replaced right into a deer (she replaced into became right into a deer through a druid). His son Oisin replaced into an awesome poet. there is not any shortage of news in celtic folklore through any potential.