When creating a phrase there are two things to think of regarding the use of a capital letter or not: firstly, whether or not to use a capital letter, and secondly to make sure that whatever decision is taken over using a capital letter, the source and target language match as necessary.
Should a phrase use a capital letter?
In general, if a phrase is short, and definitely if it is not a complete sentence, then the preference is to begin the phrase with a lowercase letter, e.g.
- a bald man
- a balloon is normally round
- a beer please
- beavers naturally build dams
- he goes
It is OK to begin a complete sentence with a capital letter, e.g.:
- He is in a hurry now. (though "he is in a hurry now" is also OK)
- May I help you, Sir? (though "may I help you, Sir?" is also OK)
- No, it's not necessary. (though "no, it's not necessary" is also OK)
- Please join the train using the nearest available entrance. (though "please join..." is also OK)
If it is a sentence it should begin with a capital letter and end with a punctuation mark.
If it is is not a sentence, then it should not have a capital letter at the start and it should not end with a punctuation mark.
It is not possible to give a fixed rule as to whether a particular phrase should use a capital letter or not, because there are so many exceptions, and there is a very large grey area in the overlap between the cases where it might be a definite "Yes" and where it might be a definite "No", so these are just guidelines.
Some more examples:
- they spent one hour (Correct, a phrase with no capital letter or end punctuation)
- They spent one hour. (Correct, since it begins with a capital letter and ends with a full stop. Note though, that although this is a valid sentence, it feels a little more like part of a longer sentence such as "They spent one hour in the café", and so here the phrase version without the capital letter or the full stop is probably to be preferred).
- They spent one hour (Incorrect. There is a capital letter at the start but no matching full stop)
Words and phrases taken from the start of a longer sentence
Words or phrases taken from the start of a longer sentence would not normally inherit the capital letter from the start of the sentence.
For example, in the sentence "First he went into a café near the station where he ate a ham sandwich and drank an Orangina.", the sentence begins with "First..." (or "D'abord" in French) with a capital letter. But notice the capitalisation of the word "first" in the breakdown or on its page. It doesn't have a capital letter. This is correct, since the word can occur in many contexts in the middle of a sentences.
The same general principle applies for phrases take from the start of sentences. For example, the first two words of the sentence "Last Saturday, Thomas went to town by bus to do some shopping with his friend Peter." form a nice phrase which can be extracted, and made into a useful phrase in its own right. But the question is, should the capitalisation be "Last Saturday" (as in the sentence) or "last Saturday"?The answer is that it should be without the capital letter, since "last Saturday" is not a sentence. If we begin the word "last" with a capital letter, then we are saying that we have a sentence, and therefore we need to end with a full stop: "Last Saturday". This is not a valid sentence.
Consistency between the use of upper or lowercase letters in the translation
Here, the golden rule is this: if one language uses a capital letter, then the translation should use a capital letter, and vice versa (unless the languages use capitalisation differently).
Example 1: if the English is "pigs live on farms", then the French MUST begin with a lowercase letter, e.g. "les cochons habitent dans les fermes" and NOT "Les cochons habitent dans les fermes".
Example 2: if the English is "May I help you?", then the French MUST begin with an uppercase letter, e.g. "Que désirez vous ?" and NOT "que désirez vous ?".
An example of where capitalisation is used differently is with the English pronoun "I" which is always written in uppercase.
Example 3: if the English is "I am 20 years old", then the French can be either "J'ai 20 ans" OR "j'ai 20 ans"