Do you separate an imperative after a conjunction by a comma?

I want you to go and ask him the price, but don't tell him I sent you.

Is this a main clause followed by a coordinating clause (imperative)?

Pour the vodka into the glass, and add orange juice.

Here, should the two following imperatives be separated by a comma?

Solution 1:

Most style guides recognize that the point of commas is to clarify meaning. Thus, Words Into Type (1974) argues as follows:

A comma should be used only if it makes the meaning clearer or enables the reader to grasp the relation of parts more quickly. Intruded commas are worse than omitted ones, but keep in mind at all times that the primary purpose of the comma is to prevent misreading.

In its discussion of compound sentences, Words Into Type notes as a general rule:

The coordinate clauses of a compound sentence are usually separated by a comma, though a semicolon may be called for by complexity of thought.

However:

The comma may be omitted if the clauses are short and closely connected in thought, especially if the connective is and; but again take care not to omit a comma that is needed to prevent the subject of the second clause being read, at least momentarily, as part of the object of the first clause.

The Chicago Manual of Style, Fifteenth Edition (2003), which opens its discussion of the comma with the comment "Effective use of the comma involves good judgment, with ease of reading the end in view," takes a fairly similar position:

6.32 Conjunctions between clauses. When independent clauses are joined by and, but, or, so, yet, or any other conjunction, a comma usually precedes the conjunction. If the clauses are very short and closely connected, the comma may be omitted.

Somewhat less open-minded is The St. Martin's Handbook, Fifth Edition (2003):

A comma usually precedes a coordinating conjunction (and, but, or, for, nor, so, or yet), that joins two independent clauses in a compound sentence. [Examples omitted.] With very short clauses, writers sometimes omit the comma before and or or. You will never be wrong to include it, however.

The New York Times Manual of Style and Usage (1999) seems even more inclined to insist on commas in compound sentences:

Commas should be used in compound sentences before conjunctions like and, but, and for: They left early, and their mother said they would arrive before lunch; The track was slow, but the betting was fast; They were impatient, for their test scores were due any day. When the clauses are exceptionally short, however, the comma may be omitted: Nero fiddled and Rome burned. Also: The comma is small but mighty.

And The Associated Press Stylebook and Briefing on Media Law (2002) has this:

The comma may be dropped if two clause with expressly stated subjects are short. In general, however, favor use of a comma unless a particular literary effect is desired or if it would distort the sense of a sentence.

All of this style-guide advice applies to compound sentences in general, regardless of whether one or both independent clauses are expressed as imperatives. And that imperatives are subject to the general guidelines should be clear from the the example of Mae West's famous line "Come up and see me some time!" The line consists of two independent instructions—"Come up [some time]" and "See me some time" but even the most comma-loving style book would be hard pressed to justify insisting that a comma be included after "up."

Because the second independent clause of the poster's first example breaks off at a sharp angle from the structure of the first independent clause, I would include the comma (if the wording had to remain the same) or perhaps reword it as follows (if not):

I want you to go and ask him the price without telling him I sent you.

In the poster's second example, I think that the comma is strictly optional from the perspective of clarity; so unless I was being governed by a particularly comma-insistent style guide, I would suit myself in including or omitting the comma.