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28.3 tudo refers to heterogenous elements, todo refers to a whole of something
Tudo is used if we refer to a group of elements, but this group of elements is considered in its totality. It shouldn't be confused with todo, because todo means whole. (And it shouldn't be confused with the Spanish todo. The Spanish todo can be used in the same context as the portuguese tudo, but as well as the portuguese todo.)
1) todo o bolo = the whole cake
2) tudo o que fazemos = everything we do / all we do
3) todos os consumidores = all consumers / every consumer
In 1) we have one single cake and we refer to the totality of this single cake. In 2) we have several things, but we refer to them as a whole. In 3) we refer to each single element. We can translate that with all, then the noun is in plural, or with everything, than the noun is in singular.
1) Tudo é mau. = All is bad. / Everything is bad
2) Todos são maus. = All are bad.
In 1) the whole situation is bad. That may have different reasons, lack of money, computer crash, bad weather. All of that contributes to get the speaker sad. There are actually several components, but the situation is considered as a whole, as a big mess. However if we have 20 strawberries in a basket and all of them are rotten, then they are all bad. In this case we focuse on the single elements, but we are talking about homogeneous elements.
Tudo is a little bit strange. It refers to single elements, that are regarded as a whole. However the meaning can be as well that one thing replaces all other things.
a) All you need is love. <=> b) The only thing you need is love. => Tudo o que você precisa é amor.
a) That's all I want.<=> b) That's all what I want. => E tudo o que quero.
In this case all is opposed to a lot of different things. Food, clothing, housing, means of transport, job, money etc.. Normally tudo can be translated with everything. However if the meaning is the only thing, then we must translate with all.
Everything can be replaced as well by all if the single elements are considered as a group. Bryan Adams for instance does everything he does for her. (That's at least what he says.) In this case everything could be replaced by all, although it is a little bit unclear whether English native speakers use it in this context.
Everything I do, I do it for you. <=> All I do, I do it for you. => Tudo que eu faço o faço por você.
If we compare the Beatles with Bryan Adams we see that everything and all are both translated with tudo, although the meaning is not the same.
1) Everything I do, I do it for you. => Tudo que eu faço o faço por você.
2) All you need is love. => Tudo o que você precisa é amor.
In 1) a lot of things are done for her. In 2) the meaning is that only one thing is needed. But if we want to keep it short and simple, we can say that tudo is everything. Tudo can only be used as pronoun and is invariable. As its opposite, nothing, it doesn't have gender and number.
Nós conversamos sobre tudo.
We talked about everything.
Você é tudo para mim.
You are everything for me.
Tudo is alway a pronoun. Todo can be pronoun and adjective. Used as a pronoun the participants of the conversation have to know what it refers to. For the reader of these lines the sentence "It's all useless" is meaningless and although the reader wants to know about what the author is talking about, the author doesn't have any intention to reveal the secret.
Used as an adjective and in plural it indicates that all elements can be the executor or the goal of the action described by the verb. In this case, obviously, the adjective has to comply in number and gender with the verb it refers to. In plural, todos / todas indicates that a totality is referred to. (todos as planetas => all plants, todo a planeta => the whole planet).
todos (maskuline, plural) / todas (feminine, plural) noun
Quando todos pensam igual, é porque ninguém está pensando.
If everybody thinks the same, nobody thinks.
Todas fazem referência a objetos que não existem.
All of them refers to objects that doesn't exist.
todos (masculine, plural) / todas (feminine, plural) adjective
Agora vocês são todos homens ricos.
Now all of you are rich.
Todas estas pessoas acreditam em mim.
All these people believe in me.
If todos / todas + noun is used as the subject or object of a sentence, there is an article between todos / todas and the noun.
todo os / todas as
A crença de que todos os homens são iguais.
It is our conviction that all human beings are equal.
Essas são todas as ferramentas que precisamos.
These are all the tools we need.
todo o (maskuline) toda a (feminine) whole
Haverá vacinação em todo o país.
The vaccination will be done in the whole country.
Envergonhaste-me em frente a toda a cidade.
You disgraced me in front of all people.
With the article o todo becomes a noun, the whole. In the example below it is easy to see the difference between various elements considered as a group and everything.
1) The whole is greater than the sum of its parts.
2) Everything is greater than the sum of its parts.
1) makes sense. An intelligent combination of different qualities is greater than the sum of these qualities. Sometime the single quality has no value at all. Ten top programmers are useless, if they don't understand the problem that should be resolved. 2) however means the exact opposite. Any single element is better than the combination.
sustantivation of todo
O todo é maior que a soma das partes.
The whole is greater than the sum of its parts.
The expression "I wish you all the best" is a little bit unclear. Perhaps the meaning is that from any good thing on earth, he wishes him the one with the highest quality. From all the choclates, the best choclate, from all bicycles, the best one, from all the smartphones, the best one etc.. But perhaps it simply means that he wishes him any good thing, not necessarily the best ones. Perhaps there is a difference between "I wish you all the best" and "I wish you everything good". In any case if we want to describe a group of elements that posseses all the same property the construction is tudo de + adjective.
tudo de melhor / bom / mal etc. all the best / everything good / everything bad etc.
Desejo a todos tudo de melhor nas próximas semanas.
I wish you all the best for the next week.
Ele disse que a culpa era minha, que mereci tudo de mal que me aconteceu.
He said, that it is my fault and that I deserve everything bad that happened to me.