Should “cum” be included in this sentence or not?

Question

I have a sentence that I need to translate:

Having left the forum with haste, ... etc

And I'm translating it as "e foro cum celeritate egressi, ..." (the rest of the sentence refers to multiple people hence why I'm using egressi) but I'm not sure whether I need to include cum in this sentence.

Does it make more sense/is it a better practice to not include cum, just leaving celeritate in the ablative on its own, so it reads e foro celeritate egressi or am I just being needlessly doubtful?

Answer 1

In this case, celeritate should be used with cum.

The general rule for the ablative of manner is that it should be used with cum if the ablative isn't modified by an adjective. Dale A. Grote explains this rule:

When the noun in this kind of construction is modified by an adjective, Latin has the option of dropping the preposition cum. This sentence could also be written: Id magna celeritate fecerunt. But if the noun governed by cum is not qualified by an adjective, the cum must be used. This is incorrect: Id celeritate fecerunt; but this is correct: Id cum celeritate fecit. And so is this: Id magna cum celeritate fecit; this is fine, too: Id magni celeritate fecit.

However, as is often the case, there are exceptions to the rule (but none that affect celeritate). According to Bradley's Arnold Latin Prose Composition, the use of cum is optional (even without an adjective) with the following:

casu "by chance" consilio "by design" consulto "deliberately"
forte "by chance" fraude "deceitfully" iure "rightly"
iniuria "unjustly" silentio "in silence" vi "by force"

There are also some common phrases with which cum is never used:

hoc consilio "with this intention"
hoc modo, hac ratione "in this way"
summo opere "ernestly, energetically"
aequo animo "calmly"
iussu tuo "at your command"
iniussu Caesaris "without Caesar's permission"
bona tua venia "with your kind permission"
nullo negotio "without trouble"
nescio quo pacto "in some way or other"

Answer 2

In concurrence with Expedito Bipes's answer, cum should be used in this sentence. Allen and Greenough's Latin Grammar states:

The manner of an action is denoted by the ablative; usually with cum, unless a limiting adjective is used with the noun.

It lists two examples, both of which conveniently use the noun in question:

1. Cum celeritate venit. He came with speed.
2. Summa celeritate venit. He came with the greatest speed.

Since there is not adjective modifying celeritas in your case, cum is to be used.