Agreed. Telma is spot on, as always.
Anyway I will give it a stab, since I feel you are in the basic level (certainly more than I am)
This depends on how you think about the sentences at hand.
Current Habits: Toby walks to work.
The author is thinking about Toby going to work everyday, he got into the habit of "walking" everyday to go to work.
Let´s say, tomorrow Toby goes by bus, car or train, so his is going to change his going to work? Certainly.
Let´s imagine that he persists for a week, or month. In a given moment, someone notices and can say "Toby goes by train to work" (RIGHT NOW, meaning HE IS is going to work everyday by train.)
It´s all about your perception at the moment you talk.
I could say "Donay comes to the English Experts." or "Donay comes to the English experts EVERYDAY."
(It´s my perception of Donay´s habit, and it doesn´t mean necessarily that he comes every single day (clocking in everyday!) No, it means that he is regularly coming here.
Permanent Situations: Carlo works in a travel agent's.
Now, the author of the sentence thinks about Carlo going to work everyday, clocking in, and all that jazz.
Means that he doesn´t generally works here (as a freelancer, perhaps), no he permanently works there.
He has contract to work there on a permanent basis/a contract basis.
It´s all about what you think at the time you are talking.
Ah, and there is a especial kind of permanent situation, that that can´t change.
Let´s pick the Toby´s example, he could change his means of transport to go to work, and would be in a permant basis. (it would use the simple present just the same, but the "why", the reason would be different).
Then there´s a case in wich this can´t be. We call this "verdades universais" because everyone knows that for a fact, that applies for ever, as long as you live (or we assume that).
Take the sentence "The earth revolves around the sun."
The earth moves around the sun.
A terra move-se ao redor do sol.
It falls on the "general truths" (verdades universais), albeit it may fall in the scientific laws as well.
You use the simple present here.
I expanded that, because you could find a question in an exame in wich you had to explain the use of them.
Like this:Match up the sentences on the right to the correct answers on the left.
A)Toby walks to work. 1)Universal truth
B)The earth revoles around the sun 2)remark habits, repeated actions or unchanged (permanent) situations.http://pt.wikibooks.org/wiki/Ingl%C3%AA ... le_presenthttp://www.solinguainglesa.com.br/conteudo/verbos.php