One of the most common problems I see in papers today is the incorrect usage of verb tense. The reasons for this problem are that English verbs function very differently from Korean verbs, and the fact that there are 12 verb tenses in English. Choosing the correct tense is vital to convey the accurate meaning, especially in scientific research. Below are some important rules to help you decide which tense to use.

#1 Citing previously published work - Present Tense

When a scientific paper has been validly published in a primary journal, it becomes knowledge. Therefore, whenever you cite previously published work you must treat it with respect. In English, we do this simply by using the present tense. For example, one should write "The world is round." not "The world was round." Here are examples of an incorrect sentence, the corrected version, and other correct sentences:

 Streptomycin inhibited the growth of M. tuberculosis (13.)

 Streptomycin inhibits the growth of M. tuberculosis (13).

 Serological tests commonly are used for the diagnosis of T. infections.

 Several recent reports (2,3,6) describe similar findings.

When an author's name is given at the beginning of the sentence and not in parentheses, either past or present tense can be used for the verb that is linked to the author. However, the verb that refers to the scientific work itself must still be given in the present tense. Please note the following examples:

 Smith (1975) showed that streptomycin inhibits growth of the disease organism. [OR]

 Smith (1975) shows that streptomycin inhibits growth of the disease organism. [BUT NOT]

 Smith (1975) showed that streptomycin inhibited growth of the disease organism.

#2: Citing published information that cannot be generalized - Past Tense

Often, results have been obtained under very specialized conditions and only pertain to the particular study being reported. Numerical data sometimes fall into this category. In this case use past tense.

 Barber (1980) reported that 28% of the 396 wasps in his study showed signs of parasitism.

#3: Referring to your own work - Past Tense

When results are unpublished including the work you are writing about it is not established knowledge. Therefore, use past tense to describe what you have done.

 In the study presented here, the drug killed 80% of the M. tuberculosis bacilli.

 Our data showed that few of the mice survived.

#4: Referring to repeated events - Present Perfect Tense

This is a difficult tense to use correctly. When observations or actions have been repeated or continued from the past to the present, present perfect tense should be used. For example:

 Nesting behavior has been studied under many environmental conditions.

 These drugs have been shown to produce significant elevations in blood pressure.

#5: Sections of a Scientific Paper

ABSTRACT/SUMMARY:	Refers primarily to the author's own unpublished results. Use mostly past tense.
INTRODUCTION:	Mostly emphasizes existing established knowledge. Use mostly present tense.
MATERIALS & METHODS and RESULTS:	Both of these sections describe what you, the author, did and found. Use mostly present tense.
DISCUSSION:	This is the most difficult section to write. The Discussion emphasizes the relationship of the author's work to previously established knowledge, so both past and present tenses are needed