argu140"During her seventeen years as a professor of botany, Professor Thomas has proved herself to be well worth her annual salary of $50,000. Her classes are among the largest at the university, demonstrating her popularity among students. Moreover, the money she has brought to the university in research grants has exceeded her salary in each of the last two years. Therefore, in consideration of Professor Thomas' demonstrated teaching and research abilities, we recommend that she receive a $10,000 raise and a promotion to Department Chairperson; without such a raise and promotion, we fear that Professor Thomas will leave Elm City University for another college."

In this argument,the author concluded that the elm city university should promote Professor Thomas and raise her salary.To justify this conclusion,the author points out that Professor Thomas has a great teaching ability because her class has the largest number of students in the university , the author also cites  the fact that the research grant Professor Thomas last two years gained had exceeded her salary to imply her competent reaserching ability.However,this argument suffers from several doubtful flaws, and is therefore unconvincing.
In the first place,the author fallaciously assumes that the great number of students in her class can show her popularity among students.Perhaps the class she teaches is not an important major course so allow more students in.Besides,even if she have a great popularity among students,there also have no evidents to show she has a good teaching ability. It's entirely possible that the good popularity because she always gives students high scores.
Secondly,The mere fact that this two years Professor Thomas has gained a exceeded-her-salary research grants is insufficient evidence to conclude that she has a strong research ability.It's quite possible that other professors have brought more.Absent the information of the comparison,the argument's conclusion about Professor Thomas' research ability is indefensible.
Finally,even assuming Professor Thomas has great abilities at teaching and researchment,the author provides no evidents that the promotion and raise is nessecery.Neither there any fact to show that Professor Thomas has the ability of management to becoming the Department Chairman,nor any evidents the author give to indicate Professor Thomas is better than other professors whos salaries are similar with hers.
In sum,this argument is unpersuative as it stands.To bolster this conclusion,the author must show that Professor Thomas is the best one  in teaching and researching and other fields thus to gain the promotion and salary raise.To better evaluate the argument,we would need more information about the comparison between Professor Thomas and other ones.