+1
These days all trains are crowded.
1 2
Comments  (Page 2) 
CalifJimWhere does it say that anywhere in the original post of this thread? It seems to me that you just made up that condition. The thread title says "affirmative to negative". It should be obvious that such a change is not possible without changing the meaning.
Though the thread title says, "affirmative to negative"; we have to deal it with grammar rules. According to the grammar, making "affirmative to negative" activity comes under "Transformation of Sentences".

It is the first rule of "Transformation of sentences" that, the form of a sentence should be changed without changing the meaning. The original sense of sentences should be protected in spite of changing its form. So I have not made up any condition. It is in grammar rules.

The reason doing behind this is, the conversation or transformation of sentence is an excellent exercise as it teaches variety of expression in writing English. It helps us to expand our uses skills by converting sentences without changing its original meaning.

Transformation of sentences contains following types of transformation

1. Sentences containing the Adverb "too"
2. Interchange of the Degrees of Comparison
3. Interchange of Active and Passive voice
4. Interchange of Affirmative and Negative sentences
5. Interchange of Interrogative and Assertive sentences
6. Interchange of Exclamatory and Assertive sentences
7. Interchange of one part of speech for another
8. Conversion of Simple sentences to compound
9. Conversation of Compound sentences to simple
10. Conversation of Simple sentences to Complex
11. Conversation of Complex sentences to Simple
12. Conversation of Compound sentences to Complex
13. Conversation of Complex sentences to Compound
CalifJim It should be obvious that such a change is not possible without changing the meaning.
We have to make it possible that is the activity which teaches us variety of expression in writing English.
sandy sandyjrThough the thread title says, "affirmative to negative"; we have to deal it with grammar rules. According to the grammar, making "affirmative to negative" activity comes under "Transformation of Sentences".It is the first rule of "Transformation of sentences" that, the form of a sentence should be changed without changing the meaning. The original sense of sentences should be protected in spite of changing its form. So I have not made up any condition. It is in grammar rules.
There is nothing about the word "transformation" that has anything to do with grammar rules. What you are probably quoting are instructions for doing a particular kind of transformation, and these instructions are from a particular grammar book with a particular approach to learning English. Don't confuse the instructions and methodology you see in one book with grammar rules. Don't confuse the rules for doing an exercise with the rules of English grammar.

Due to the fact that these conditions about "transformation" are specific to the methodology in your book, you need to make these conditions clear when you post your questions. No one else except the readers of that particular book knows that the transformations that you are inquiring about are supposed to be meaning-preserving transformations unless you tell them so.

CJ
Students: We have free audio pronunciation exercises.
These dags all trains are crouded

eg These days no trains are crowded.

eg These dags all trains have plenty of vacant seats.

These days no trains are uncrowded.
Teachers: We supply a list of EFL job vacancies