Flick back to the Basics 1 tips notes page! Remember that Irish has two versions of the verb to be - and similarly two versions of the verb to not be.
You use is and ní for classification/identification - in other words, to say what class or group something belongs to.
- Is buachaill é He is a boy
- Ní póilín í She is not a police officer
- Is aisteoir é an fear The man is an actor
- An é gunna é? Is it a gun?
By comparison, you use tá and níl to describe something, or to explain what state it is in at the moment.
- Tá an buachaill mór The boy is big
- Níl an póilín ag ithe The police officer is not eating
- Tá aisteoir ar an stáitse An actor is on the stage
- An bhfuil gunna ag an saighdiúir? Does the soldier have a gun? (literally "Is [there] a gun at the soldier?")
In this sentence, we are describing the creature's current state - literally, "A turtle is not at me" - so we use Níl.
If instead we were classifying the creature itself - for example, something like "The turtle is not a fish" - then we would use Ní instead: Ní iasc an turtar.