These are two parts which can be argued to be ambiguous in A Modest Proposal, but there are many others.
1)
Let's look at this passage:
These mothers, instead of
being able to work for their honest livelihood, are forced to employ
all their time in strolling to beg sustenance for their helpless
infants.
It's ambiguous here whether the speaker actually means the critique towards the mothers (since work is in the end, more beneficial than begging) or whether the speaker is ironic here.
2)In the following passage:
that it will prevent those voluntary abortions, and that horrid practice of women murdering their children,
it is ambiguous, because while it would stop mothers killing their children, the children would be killed anyway: so the call to stop murdering children cannot be taken at its face value.
