DISCLAIMER: This was my own observation. If any of you know that this down here is completely wrong… PLEASE correct me quicky so I can get this idea out of my mind.

When I started the い-Adjectives chapter, I was quite confused on how you can conjugate a verb. But now I’ve figured it out, so I just felt like sharing my vision on this.

The difference between conjugating with です　and the adjective, is that です changes the tense of a noun / the whole sentence, and conjugating the adjective, changes the tense of the adjective itself, and NOT the noun. I think an example will make it more clear:

PRESENT – The tall building is… / The building, that is tall, is…
PRESENT – たかいたてものは。。。です

PAST 1 – The tall building was… / The building, that IS tall, WAS…
PAST 1 – たかいたてものは。。。でした

PAST 2 – The building, that WAS tall, IS…
PAST 2 - たかかったたてものは。。。です

You see what happened here?

In the first past tense, you’re saying that the building is still tall, but something happened to it in the past. In the second past tense, you’re saying that the building USED to be tall, but something is happening to it in the present.

How you conjugate the noun vs the adjective changes the meaning of a sentence.

If you change the noun to ”the building(noun), that is/was/isn’t/wasn’t tall (adjective), is/was/isn’t/wasn’t … you’re making it easier for yourself to understand.

I hope this clears things up (and I hope that I’m not all wrong here, too… it was my own observation after all).