Our panel of 91 professional philosophers has responded to

5
 questions about 
Euthanasia
39
 questions about 
Race
34
 questions about 
Music
75
 questions about 
Perception
51
 questions about 
War
282
 questions about 
Knowledge
574
 questions about 
Philosophy
208
 questions about 
Science
117
 questions about 
Children
69
 questions about 
Business
218
 questions about 
Education
154
 questions about 
Sex
75
 questions about 
Beauty
24
 questions about 
Suicide
27
 questions about 
Gender
1280
 questions about 
Ethics
287
 questions about 
Language
170
 questions about 
Freedom
36
 questions about 
Literature
284
 questions about 
Mind
80
 questions about 
Death
2
 questions about 
Action
374
 questions about 
Logic
43
 questions about 
Color
124
 questions about 
Profession
58
 questions about 
Punishment
4
 questions about 
Economics
89
 questions about 
Law
70
 questions about 
Truth
221
 questions about 
Value
2
 questions about 
Culture
88
 questions about 
Physics
68
 questions about 
Happiness
77
 questions about 
Emotion
110
 questions about 
Biology
32
 questions about 
Sport
31
 questions about 
Space
54
 questions about 
Medicine
96
 questions about 
Time
58
 questions about 
Abortion
244
 questions about 
Justice
110
 questions about 
Animals
67
 questions about 
Feminism
392
 questions about 
Religion
81
 questions about 
Identity
23
 questions about 
History
105
 questions about 
Art
151
 questions about 
Existence
134
 questions about 
Love

Question of the Day

Like you, I'm puzzled by the form of the conditional "Only if A, then B." It doesn't seem to be idiomatic English. One might say "Only if you go to the party will I go," but one wouldn't say "Only if you go to the party, then I will go." That would be unidiomatic. So I presume that the conditional form you're learning is "Only if A, B" rather than "Only if A, then B." I would interpret "Only if A, B" as stating that A is a necessary condition for B, and therefore implying that B is a sufficient condition for A.

If one wants to say that A is both necessary and sufficient for B, then one can say "If and only if A, B" -- although "A if and only if B" would be a smoother way of saying it. In any case, make sure that your logic teacher really did say "Only if A, then B" and, if so, ask if he/she meant to say "Only if A, B."