Ubi consensus de argumento deest, dissensio statim apparet.

Ubi literally means where, but in a sentence like this it can also be understood more generally as wherever or when(ever).

So here it introduces the circumstance in which the main statement is true:

• Ubi consensus de argumento deest = Where / whenever agreement about the issue is lacking

Because the sentence expresses a general truth, English may translate it in more than one natural way.

It has two parts:

• Ubi consensus de argumento deest = a subordinate clause introduced by ubi
• dissensio statim apparet = the main clause

So the overall pattern is:

• When/where X is lacking, Y appears.

Latin often puts the subordinate clause first to set the scene before giving the main point.

Consensus is a noun meaning agreement, harmony, or unanimity.

In this sentence it is:

• nominative singular
• the subject of deest

So consensus ... deest means agreement is lacking.

A learner may wonder whether consensus is plural because of the ending, but it is not. Here -us is a singular noun ending.

Argumento is ablative singular.

It is ablative because it follows the preposition de, and de normally takes the ablative case.

So:

• de argumento = about the issue / about the subject / concerning the point under discussion

This is one of the most basic preposition patterns in Latin:

• de + ablative

It most naturally goes with consensus:

• consensus de argumento = agreement about the issue

So the clause means:

• agreement about the issue is lacking

A learner might wonder whether de argumento is somehow required by deest, but here it is better understood as modifying consensus, telling you what the agreement is about.

Deest means is lacking, is absent, or is missing.

It is the 3rd person singular present of deesse, a compound of esse (to be). So it is related to est, but with the added sense of absence or lack.

That is why Latin uses deest instead of something simpler like non est:

• non est = is not
• deest = is lacking / is absent

So consensus ... deest is a more precise way to say that agreement is not present.

Dissensio means disagreement, dissension, or difference of opinion.

In this sentence it is:

• nominative singular
• the subject of apparet

So:

• dissensio statim apparet = disagreement immediately appears

It is also nicely paired with consensus:

• consensus = agreement
• dissensio = disagreement

Apparet means appears, becomes visible, or more idiomatically becomes evident / shows itself.

So dissensio statim apparet can mean not only that disagreement literally appears, but also that it quickly becomes obvious.

That is often how apparet works in Latin: it can refer to something becoming clear, not just something physically coming into view.

Statim is an adverb meaning immediately, at once, or right away.

It modifies apparet:

• statim apparet = immediately appears

Latin word order is flexible, so statim comes before the verb here, but in English we may place it in different ways:

• disagreement immediately appears
• disagreement appears immediately
• disagreement appears at once

All of those can express the idea.

Both deest and apparet are present tense because the sentence states a general truth.

Latin often uses the present for statements like:

• Whenever this happens, that happens
• Where this is lacking, that appears

This is sometimes called the gnomic present or general present. English does the same thing:

• When trust fails, conflict grows
• Where agreement is lacking, disagreement appears

Because this sentence is simply stating a fact or general truth, not a doubtful, imagined, or strongly dependent idea.

So Latin uses the indicative:

• deest
• apparet

With ubi, the indicative is very normal when the speaker means when/where this actually happens. There is nothing especially hypothetical here.

Because Latin has no articles.

So consensus, argumento, and dissensio can be translated in English as:

• agreement
• the agreement
• an agreement

depending on context.

Here English will usually use a more general phrasing, such as:

• Where agreement about the issue is lacking, disagreement immediately appears.

Latin leaves that choice to the reader and the translator.

Not necessarily, and probably not here.

Latin argumentum often means:

• subject
• topic
• theme
• point at issue
• line of reasoning
• proof

So de argumento here is best understood as about the issue or about the subject under discussion, not necessarily about a fight.

That is a useful false-friend warning for English speakers: Latin argumentum is often broader and more intellectual than the everyday English word argument.

Yes. The sentence is built on a clear contrast:

• consensus = agreement
• dissensio = disagreement

This gives the sentence a balanced, almost proverbial feel:

• when agreement is absent, disagreement shows itself

Latin often likes this kind of neat opposition, especially in compact, aphoristic statements.