Siquiera vs hasta
 

Hi,

Both words are used for even; I've got a strong impression that they are far from being interchangeable, though. On the other hand, I can't figure out how to use them properly.

You're right that they are not interchangeable. Here are a couple of examples:

¡No quiero ni siquera ir! = I don't even want to go!
Camina hasta que llegues a la esquina. = Walk until you reach the corner.

I mean a slightly different usage:

No tengo el menor sentido empresarial, y hasta Tom lo dice
I have no business acumen, and even Tom says so.

Is it possible to recreate the sentence using siquiera?

No. When 'even' means 'up to' and/or 'including' only hasta (or its synonyms aun and incluso) can be used.

When 'not even' is the meaning, use ni siquiera.

Using siquiera by itself (without ni) means 'even though' or 'even if'.

As you can see, hasta and siquiera are never interchangeable.

Thanks!

"Even" as "hasta" expresses that something happens to a certain degree, or it's used as an intensive. In this case, "hasta" is mostly synonymous of "incluso".

- Estaba tan enojado, que hasta fue a mi casa a reclamarme.
- He was so mad, that he even went to my house to complain to me.

- La idea es tan ridícula que hasta pensar en ella da vergüenza.
- The idea is so ridiculous that even thinking about it is cringeworty.

- El pájaro estaba tan enfermo que se negaba hasta a beber agua.
- The bird was so sick, that refused to even drink water.

- El Capitán dijo: "¡Hasta yo entendí esa referencia!"
- The Captain said: "Even I understood that reference!"


"Even" is never "siquiera", but "not even" can become "ni siquiera":

- Me escondí tan bien, que ni siquiera me vieron.
- I was so well hidden, that they didn't even see me.

- ¿Ya te vas y ni siquiera un beso me vas a dar?
- You're already leaving and you're not even giving me a kiss?

- ¡Ni siquiera lo pienses!
- Don't you even think about it!

- Es tan burro, que ni siquiera sabe escribir bien su nombre.
- He's so stupid, he can't even spell his name right.