Timothy wrote:(Timicus lamentat)
§95 II.
"Alto muros, longa at dura bella, clara victorias quis non laudat?"
Isn't "victorias" the accusative plural of victories? So I translated this as "famous victories" rather than "famous battles" (claras pugnas).
I assume the book has
altos muros and
claras victorias. You are correct that
victoria means "victory", does the key have otherwise?
(sigh) The previous set of excercises really threw me. I must have gone over §86 10 times without getting it right. I've had a lot of difficulty selecting the proper case for phrases such as "to the village", "call to dinner" to the point where I couldn't tell what the object of the sentence was any longer or if I was just memorizing the the answers by sheer repetition. I finally stopped and did some remedial Latin from BLBCD and then went back and tried again.
I think I have gotten past it since I was finally able to complete the exercise while selecting the right words, matching cases, and knowing why. However, it consummed a lot of time.
It's good to go back and review everything that seems confusing. To be able to read, you have to recall all the old concepts and merge them with newer ones. Hopefully, BLD integrates old material with new material well, and you just have to keep it all by memory.

In any case, my question: does "ad" _always_ use the Accusative rather than the Ablative? §53 lists the prepositions that must have the Ablative case following but I can't see why "ad" takes the Accusative other than by default. That's where I get into trouble.
Yes,
ad is a preposition that always takes the accusative. The flaw in most textbooks is that they tend to explain the ablative as the case of prepositions, when this is not really true.
Prepositions that take the ablative are mainly motion away (e.g.
ex, ab, de) and action without change in position (e.g.
sub, in + abl.). The ablative by itself can carry meanings of separation, moving away, and other similar relationships.
Prepositions that take the accusative usually deal with motion towards or against an object, and sometimes relative positions.
Ad is the most obvious example for motion towards, since it truly does mean "towards". Other examples of motion towards are
in+acc. "into...",
sub+acc. "under... (in motion)", and
secundum "following...". Ideas of relative position, except for those that describe separation and motion away (which are governed by ablative), are expressed by such prepositions as
circum "around...",
super+acc. "over...", and
citra "on this side of...".
You have to remember which case to use for each preposition, and these rules should help you do so, but you will have to memorize the cases nonetheless.
...nautam vocat.
But when I try to put in "to dinner" I get stuck with using the accusative because I already have a direct object.
The object of a preposition is not the direct object of the sentence. You will know them apart because the direct object stands alone and the prepositional object has a preposition before it

This will be hard to do if you skip through sentences looking for subject, verb, and object like many people, so try to read it in the order it is written and recognize the parts in their natural state.
Lastly, I always though Latin was a definative language such that there shouldn't or couldn't be abiguity in terms of word connections; hence the word order could be used for emphasis. But I just came across the thread on amici legati mali. ugh. I didn't have the problem when I did the exercise, but now I'm not so sure.
Why do beginner books do this sort of thing?
With fragments there are far too many interpretations. You need the entire sentence to distinguish whether this is...
1.) nominative plural
amici and genitive singular
legati mali the friends of the bad legate
2.) genitive singular
amici and genitive singular
legati mali the bad legate's friend's...
3.) genitive singular
amici and nominative plural
legati mali the bad legates of the friend
In Sentence 1, the subject is the plural noun "friends", so the verb must also be plural. In Sentence 2, the subject has not yet been revealed. Sentence 3 would take a plural noun like Sentence 1, and you would have to distinguish which made more sense (probably Sentence 1, but depends on context).
This is by far more precise than English, where a word such as "friend" could be any singular case other than genitive, and "friends" could be any plural case except for genitive, while in Latin all the words were narrowed down to genitive singular or nominative plural.
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae