I guess no one else is posting their responses up for the assignment? (common little lemmings you know you can fly!...) Well perhaps someone needs to leap first. So, I'll post what I have for the first question up, and the rest of the questions as comments to the already placed posts. If anyone thinks I'm plainly wrong, have made things to convoluted, etc. LET ME KNOW. If people don't let others know where they go wrong, or where to make some revisions to their arguments, then ya' can't improve. So, on to question:
a. Argument from Paraphrase:
(1) I believe permissible paraphrases of ordinary language.
(2) I believe permissible paraphrases of ordinary language of what I believe.
(3) Ordinary language permits the paraphrase: there are many ways that things could have been, besides the way they actually are.
(4) (3) is a sentence of existential quantification; that there are entities of a certain description (“ways things might have been”).
(5) So, I believe that there are entities of a certain description (“ways things might have been”).
Hopefully this is a valid re-construction of the argument. The truth of the conclusion follows from the truth of the premises in virtue of the argument's form, so all good. But, premise (4) seems glaringly false, therefore making the argument unsound. I don't think (4) is on the face of it paraphrased properly as a sentence of existential quantification from (3). Unfortunately it is difficult to pinpoint why, but I'll give it a shot.
In (3) the phrase “there are many ways that things could have been” the emphasis is placed strictly on the ways. It is about the ways things are, or could be. In (4) the phrase “there are entities of a certain description (“ways things might have been”)”, there is a doubling of things emphasis. (4) could be rephrased as: “there are things of a certain description (“ways things might have been”). In a sense there in a conjunction of emphasis in this phrase. First, there are things of a certain description, and second, there are ways these things might have been. So, (4) is not a strict paraphrase of (3). It is something extra, plus a paraphrase of (3). Where the something extra is the thing, not just the way it is or could be.
b. Argument from Philosophical Utility:
(1) If an ontological hypothesis (GR) has sufficient and greater net utility than its rivals, then GR has eminent utility.
(2) The ontological hypothesis (GR) has sufficient and greater net utility than its rivals.
(3) So, GR has eminent utility.
(4) If an ontological hypothesis (GR) has eminent utility, then that gives us good reason to believe that GR is true.
(5) So, we have good reason to believe that GR is true.
This also seems to be a valid re-construction. (2) and therefore (3), seem false or rather, yet to be proven. Or as Bricker would say “wishful thinking” in possibilia. For Bricker, possibilia provide both the requisite objects that intentional states are about, and the requisite domains over which modal operators range. So Bricker takes “the existence in possibilia to be a prerequisite”. Now, taking what Lewis says in Counterfactuals, it seems that his criteria in favour for the sufficient and greater utility of GR (or eminent utility), is that it's possibilia, or sentences concerning, “should be taken at their face value unless (1) taking them at face value is known to lead to trouble and (2) taking them some other way is known not to.” In a sense, I think Lewis is making a stronger claim than Bricker. Namely that: The ontological hypothesis (GR), that possibilia exist, is true iff GR has sufficient and greater net utility than its rivals, i.e. taking them at face value is not known to lead to trouble and not taking them some other way is known not to.
I realize this is a messy biconditional, but, that is what Lewis seems to want for (2). Unfortunately, I cannot see a way in which the right-hand of the biconditional can be satisfied, unless an appeal to wishful thinking is made just as Bricker (though I should mention that I don't agree with his motivations for realism either), states. And perhaps this is more of a reflection on myself, but, I do not defer to the glass being half full of utility juice, unlike Lewis.